#!/usr/bin/perl -w
use 5.016;

# rounded-1079543.pl - Round to 2 decimal places using regexen 
#                     (even though printf/sprintf would be preferred) 
#             update 2: as Laurent_R notes, this is truncation, not rounding.
#                       but it is what OP asked for.

my $num =  3.333333333;
$num =~ /(\d*\.\d{2})/;
my $roundednum = $1;
say $roundednum;

  # or

my $num2 = 5.5555555;
$num2 =~ s/(\d*\.)(\d)(\d).*/$1$2$3/;
my $rounded2 = $num2;
say $rounded2;

=head execution:

C:>rounded-1079543.pl
3.33
5.55
=cut