Here's one way to do it, with help from the Number::Format module.

#!/usr/bin/env perl

use strict;
use warnings;

use Number::Format;

while(<DATA>) {
    chomp $_;
    my $x = new Number::Format;
    my $formatted = $x->format_number($_, 1, 1);
    $formatted = sprintf("%.2f", $formatted);
    print "$_ -> $formatted\n"; 
}

exit;

__DATA__
1.24
13.25
2.90
2.99
2.92
14
[download]

Output:

1.24 -> 1.20
13.25 -> 13.30
2.90 -> 2.90
2.99 -> 3.00
2.92 -> 2.90
14 -> 14.00
[download]