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";
}