An individual Wal Mart Store has multiple payment processing things going on. It is possible to literally make a purchase at 1:00 PM at a Supercenter for $25 and have it code as Grocery, then make another purchase at the same Supercenter store at the same register with the same card at 1:01 PM for $25 again and it will code as Discount/General Merchandise.

I don't count on Wal Mart purchases to ever work for any bonus at a Grocery Store/Supermarket because they are too unpredictable.

I have not experimented enough with Neighborhood Market units to see how those code or if they do consistently code grocery...

Smart & Final codes grocery.

If you go to OR/WA/ID, Kroger owned Fred Meyer which is like Wal Mart, also codes as grocery.

If you need gas, a Safeway (Vons) gas station will code as Grocery IF you pay the clerk for the gas (do not pay at the pump). Beware you must go see the clerk after fueling if you do not fuel the entire amount, they may give you cash back or they may credit the card (supposed to credit the card, but the register doesn't force that to happen...).