my $n; $n += 0.1 for 1..10;          # $n = 0.1 * 10 = 1  ...ish
my $r = int($n*2)/2;

print("round($n) = $r\n");           # round(1) = 0.5
print("cause it's really doing\n");  # cause it's really doing
printf("round(%.16e)\n", $n);        # round(9.9999999999999989e-001)