While CentOS 6 will have Perl 5.10.* supported (see the list of included packages for Red Hat Enterprise Linux 6), there are not many RPM sources for installing 5.10.x on CentOS 5. Your best bet will be to compile it yourself.
To do that, you can download any version from 5.3 to the latest development version (5.13) from CPAN - you can download it directly from here.
Download, extract, configure if you want to support specific features, and run
make test, and
make install. See the installation page for Perl at CPAN here for a walkthrough (You can also see a basic tutorial for installing 5.10 this way at this site).