I tried it with 1/3:

#! /usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

sub amnt {
    my ($amount) = @_;
    say "$amount I'm checking amount before padding";

    my $padamnt = sprintf("%016d",$amount);
    say "$padamnt I'm checking amount after padding";
}

amnt(1/3);
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As expected, before padding its 0.333333333333333, after padding it's 0000000000000000. Rounding.

Now try it with 1.999999999999999. print doesn't output the precise value.

2 I'm checking amount before padding
0000000000000001 I'm checking amount after padding
[download]