I believe that if not specified, the default number of rounds is 5000.
I edit /etc/default/passwd  and /etc/pam.d/password , to be sure and hope for the best. I also add these lines , taken from the Debian version of the file, to /etc/login.defs.
I've been doing this for about a year or so and I always wondered why the default in Archlinux was to use MD5 in /etc/pam.d/passwd and DES in /etc/default/passwd. I see that using DES in /etc/default/passwd is still the case.