Yes, Wal-Mart does allow cash back at the register when you purchase something with your debit or credit card.  The cash back requires a pin to be entered most of the time.  Target also does this where they allow people to get cash back.  Wal-Mart allows up to $50 back, and Target allows up to $40 back.

The cash back at register is better than you going to an ATM that is not from your bank and being charged $2 to $4 in addition to your own bank charging you $2.

Wal-Mart cash back amount