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) {
    $total += $count{$datum};
    $percentile{$datum} = $total / @data;
}