\define@key{Gin}{resolution}{%
  \pdfimageresolution#1\relax
}%

\documentclass[border=5pt]{standalone}
\renewcommand{\familydefault}{\sfdefault}
\usepackage{siunitx}
\sisetup{detect-all}
\begin{document}
\begin{tabular}{l}
$\mathrm{10\sp5}$\num{e5} this is a test\\
{\rmfamily$\mathrm{10\sp5}$\num{e5} this is a test}
\end{tabular}
\end{document}

\documentclass[border=5pt]{standalone}
%\renewcommand{\familydefault}{\sfdefault}<-----------
\usepackage{siunitx}
\sisetup{detect-all}
\begin{document}
\begin{tabular}{l}
$\mathrm{10\sp5}$\num{e5} this is a test\\
{\rmfamily$\mathrm{10\sp5}$\num{e5} this is a test}\\
{\sffamily$\mathsf{10\sp5}$\num{e5} this is a test}\\
\end{tabular}
\end{document}

(font-lock-add-keywords
 nil
 `(
   ;; macros that don't match the below patterns aren't kosher;
   ;; signal warning
   (,(rx (group "\\" (+ (any alpha "_"))))
    (1 font-lock-warning-face t))

   ;; macros that use @ are bad!
   (,(rx (group "\\" (* (any alpha))
                "@" (+ (any alpha "@"))))
    (1 font-lock-warning-face t))

   ;; standard macros are okay though
   (,(rx (group "\\" (+ (any alpha))))
    (1 font-lock-string-face t))

   ;; literal spaces
   ("~"
    (0 font-lock-comment-face t))