This answer by Roy Johnson improved this answer by wrvhage by dealing with negative numbers. This answer adds an improvement to handle the case where decimal places is zero, i.e. by not including the hanging decimal point, e.g. "10.1" rounded to zero places would become "10." instead of "10". Any other changes are just rearrangement of the code.

sub stround
{
  my ($n, $places) = @_;
  my $abs = abs $n;
  my $val = substr($abs + ('0.' . '0' x $places . '5'),
                   0,
                   length(int($abs)) +
                     (($places > 0) ? $places + 1 : 0)
                  );
  ($n < 0) ? "-" . $val : $val;
}
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