Since you don't really need to know what the exact sides are, why not let perl do most of this for you?

use strict;
use Carp;

my ($l, $r, @err) = split /\./, $test;

carp "oops, more than 2 \.'s.\n" if @err;

if ($l) {
   if ($r) {
      #handle case of rational dollars
   } else {
      #handle case of integer dollars
   }
} else {
   carp "oops, we don't even have a dollar!\n";
}
[download]

This seems like it'll cover more cases than you currently have (never trust your user) and it seems a bit easier as well...

HTH,
jynx

ps if another monk can spot errors please do so, it's early and i haven't had my coffee yet...