\documentclass{article}
\usepackage{fp}
\usepackage[plain]{automultiplechoice}
\begin{document}
\makeatletter

\def\test@section{}
\newcommand{\testsection}[1]{\def\test@section{#1}\message{^^JSECTION(#1)^^J}}
\newcommand{\test}[2]{%
\message{^^JTEST(#1,#2)^^J}%
}

\newcount\r

\testsection{Significant::base10}

\AMCsignificantDigits{2}{1.2345}{\r}
\test{\the\r}{12}

\AMCsignificantDigits{2}{0.034345}{\r}
\test{\the\r}{34}

\AMCsignificantDigits{2}{10789.5}{\r}
\test{\the\r}{11}

\AMCsignificantDigits{3}{-25678.56}{\r}
\test{\the\r}{-257}

\AMCsignificantDigits{1}{0.0065}{\r}
\test{\the\r}{7}

\AMCsignificantDigits{1}{-0.0065}{\r}
\test{\the\r}{-7}

\AMCsignificantDigits{2}{0.996}{\r}
\test{\the\r}{10}

\AMCsignificantDigits{1}{-9.76}{\r}
\test{\the\r}{-1}

\AMCsignificantDigits{3}{0}{\r}
\test{\the\r}{0}

\testsection{Significant::base2}

\AMCsignificantDigits[2]{3}{-643}{\r}
\test{\the\r}{-5}

\AMCsignificantDigits[2]{4}{2345}{\r}
\test{\the\r}{9}

\AMCsignificantDigits[2]{2}{7632}{\r}
\test{\the\r}{2}

\AMCsignificantDigits[2]{3}{0}{\r}
\test{\the\r}{0}


\end{document}

