#!/usr/bin/perl
use strict;
use warnings;
use POSIX;

my $num = -1.2;
my $rounded_pos = (POSIX::floor($num*2))/2;
my $rounded_int = (int $num*2)/2;

printf "Rounded is %.1f for %f using POSIX\n", $rounded_pos, $num;
printf "Rounded is %.1f for %f using int\n", $rounded_int, $num;

__END__
Output:
Rounded is -1.5 for -1.200000 using POSIX
Rounded is -1.0 for -1.200000 using int