# round(789.456,-2) => 800
# round(789.456,-1) => 790
# round(789.456)    => 789
# round(789.456,1)  => 789.5
# round(789.456,2)  => 789.46

sub round {
  my ($n, $p) = @_;
  my $sign = ($n > 0) ? 1 : -1;

  $p ||= 0;
  $n *= 10 ** $p;
  $n = int($n + .5 * $sign);
  return $n / 10**$p;
}