The POSIX module is part of the standard distribution and has both ceil and floor() functions.

#! perl -sw
use strict;
use POSIX;

my $n = 5.2;

print $n, ' ', POSIX::ceil($n), ' ', POSIX::floor($n), $/;

__DATA__
C:\test>203372
5.2 6 5

C:\test>
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