You asked this question on money@SE, and seems like you've deleted it?

I did. It had been downvoted and there were comments that it was off-topic there. Searched and thought this looked more fitting since it is about what law might be anywhere in the world which covers this.

While this isn't relevant to your question about places that require listing the final price and having different tax rates, there are places in the us where a city crosses county/state lines and stores on the different side of a street can have different tax rates which makes knowing the final price much more confusing.

@JoeW, confusing... perhaps. I used to get frustrated that they didn't just advertise the "final" cost to the customer, but I've flipped my opinion on the matter because keeping tax separate raises awareness of what the government is taking. It was due to a specific incident: Washington state implemented a "carbon fee" which resulted in a $.46/gallon increase in the price at the pump. When consumers began to complain, stations began posting the portion of the cost attributed to this fee, and natural gas utilities made note of it on their invoices, which the state then banned doing!

Different jurisdictions do things in different ways… what else is there to this?

VAT and sales tax are not the same thing and are treated very differently

@RobbieGoodwin, "Different jurisdictions do things in different ways…" That is acknowledged in the question, so what's your point?

@MichaelHall The point was that the Question negated itself by accepting different jurisdictions doing things in different ways…

@littleadv, I don't really doubt that VAT and sales tax are not the same thing and they might well be treated very differently, yet I'd hoped you could tell us how they differ in nature or treatment?

@RobbieGoodwin that would probably be a separate question, but one major difference is the "A" part. VAT applies only to the added value, while sales taxes usually apply to the sold item based on the sale price.

@RobbieGoodwin, No, it didn't negate itself. If a state required vendors to incorporate sales tax into a final advertised price, yet each county imposes a different tax rate, the price for the same item would vary depending on the county. The OP is asking whether such a situation exists, and how a company might deal with statewide advertising. i.e. which price would you advertise? (the latter is a business question...)

Whether or not it is a wise policy, the almost universal practice in the U.S. (with only a handful of exceptions usually for entertainment or public fair circumstances where prices are quoted in round after tax dollars) is that prices are quoted on a sales tax exclusive basis. But some excise taxes (e.g. on gasoline and liquor, but not plane tickets or phone service) are included in the quoted price. Most ads quoting prices to a general audience in the U.S. also state that "prices may vary" at a particular store, and some prices vary often gasoline prices are rarely advertised.

@MichaelHall What you said was both true, and irrelevant. What buyer can you think of who cares about anything but the final cost including price, tax and anything else? Unless both price and difference in tax rates are large and the state border is close, how many buyers are likely to go elsewhere? That's why here in the UK, retail prices are always inclusive and no, it doesn't matter which part of the UK you're buying in.

@littleadv Thanks and while that's doubtless true, how does it change what I just explained to MichaelHall ?

@RobbieGoodwin, you are missing my point, as well as what the question is actually asking.

@RobbieGoodwin have no idea what you explained to whom

@MichaelHall So I might be, and I'm suggesting that while what you say is true, it's not helpful… in fact, it's unhelpful… to the Question.

@littleadv You would, if you looked back aComment or three. Is that unreasoinable?

I commented on the question for the OP, why do I need to follow your discussion with someone else?

@RobbieGoodwin, "I'm suggesting that while what you say is true, it's not helpful… in fact, it's unhelpful… to the Question." That was my reaction to your first comment in this thread. I don't see any use in continuing...

@MichaelHall Good for you. Carry on paying unstated taxes on top of largely meaningless 'prices' and trying to work out the extra as you go… and please recognise that while that's your choice, it will always be more of an inconvenience than any kind of benefit to you.

Just as a note to your salient point about prices varying in the US, sales tax can vary not only by state but also by locality within a state. And often, the price on advertisements is the "manufacturer's suggested retail price" (MSRP) which may not be the price at a given retailer.