I knocked up a module, probably my first ever, to do rounding. I used POSIX::ceil() and POSIX::floor() to a recipe I saw in a C text book. Written before I knew about strict and warnings, I'm afraid; I'll have to revisit it one day.

package Rounders;
use Exporter;
@ISA = ('Exporter');
@EXPORT = qw(rndZero rndPlaces);
use Carp;
use POSIX qw(ceil floor pow);

sub rndZero
{
    my($val) = shift;
    my $rounded = $val < 0 ?
       POSIX::ceil($val - 0.5) : POSIX::floor($val + 0.5);
    return $rounded;
}

sub rndPlaces
{
    my($val, $places) = @_;
    my $rounded = rndZero($val * POSIX::pow(10.0, $places)) /
       POSIX::pow(10.0, $places);
    return $rounded;
}

1;
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Calling like this

$toNearest100 = rndPlaces(1234.56, -2);
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would result in $toNearest100 getting a value of 1200.

Cheers,

JohnGG