Actually I currently deliver for lowes and they have no such rule against tipping. It certainly is not mandatory but always welcomed. What a team can be fired for is asking for a tip or "tip baiting" (which is doing something like placing 5 bucks on the clipboard that the customer signs.). Personally If my job consists of dropping something off in a box or in a garage a tip really isn't expected. If I bring that 300lb fridge to the 3rd floor for you I certainly wouldn't turn down the tip
. So basically it's up to you. As for companies that do not allow tipping, that will certainly be notated in your paperwork from the store. The best of my knowledge only best-buy does not allow tipping.