$ perl -e'printf "%-3s %2d\n", "$_:", $_ - ($_ % 5) for 0..19' 0: 0 1: 0 2: 0 3: 0 4: 0 5: 5 6: 5 7: 5 8: 5 9: 5 10: 10 11: 10 12: 10 13: 10 14: 10 15: 15 16: 15 17: 15 18: 15 19: 15