It can be done with less division.

Notice 0, 1 and 2 round to 0. While 3 and 4 round up to 5. Using this knowledge, examine the number modulus 5. If its below 3 round down, otherwise round up.

Also I agree with the other comment, your examples are a bit off. For example both 33 and 36 round to 35.

use warnings;
use strict;

sub round5 {
    my ($number) = @_;

    my $remainder = $number % 5;

    if ($remainder < 3) {
        return $number - $remainder; 
    } else {
        return $number - $remainder + 5;
    }
}

for (0..10) {
    print "$_ rounded is " . round5($_) . "\n";
}
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