The umask 002 should be working (assuming you're not doing anything daft like trying to use permissions on a filesystem type like FAT that doesn't support them).
What do you see if you do a
ls -l testfile
If that works as expected, then it must be down to how the files are being created.
By the way, if you haven't already then you probably want to do a
chown root:sales /home/sales
chmod g+s /home/sales
in order to enforce the setting of the correct group on all new files/directories created under that directory.