#!/usr/bin/perl

use strict;
use warnings;

use POSIX qw /ceil/;

my @data = qw /1 2 4 5 9 10 99 100 110 124 125 900 999 1000 1100/;

foreach (@data) {
    my $frac = $_ < 100 ? 5 : (1 . ("0" x (length ($_) - 1))) / 4;

    my $new = $frac * ceil ($_ / $frac);

    print "$_: $new\n";
}

__END__
1: 5
2: 5
4: 5
5: 5
9: 10
10: 10
99: 100
100: 100
110: 125
124: 125
125: 125
900: 900
999: 1000
1000: 1000
1100: 1250