The fact that the digits near the end are changing on you should throw up a red flag in your mind. Consider the following case; the code

#!/usr/bin/perl
use strict;
use warnings;

printf "%.2f%s", "4212412124124124.10623", "\n";
printf "%.2f%s", "12412124124124.10623", "\n";
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outputs the result

4212412124124124.00
12412124124124.11
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You are exceeding machine precision on your decimal. See What Every Computer Scientist Should Know About Floating-Point Arithmetic for background.