oh, below, not below or equal. Just switch the order of the two statements in the last loop. I usually only do the *100 when it's time to print, but I added it for you.

use strict;
use warnings;

my @data = get_data(); # or however you get them

my %count;
foreach my $datum (@data) {
    ++$count{$datum};
}

my %percentile;
my $total = 0;
foreach my $datum (sort { $a <=> $b } keys %count) {
    $percentile{$datum} = $total / @data * 100;
    $total += $count{$datum};
}
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