God tipping confusion really annoys me. I don't get tipped when I do a good job- why are there some jobs which apparently do expect tips?
Surely if you've arranged a service (eg, sat down in a restaurant, paid for a supermarket delivery) then the price quoted includes having the food brought to you- because the person doing that job is worthy of being paid for actually doing it?
Obviously there is some minimum standard here- so if your waitress gets your order spectactularly wrong, or the delivery driver chucks your food over the back fence, then they haven't done their job properly. But then you'd take it up with the manager or whoever and expect a refund for a service you hadn't received- and they would deal with it accordingly from their end.
As far as I'm concerned if I go out to eat, the price on the menu includes the cost of the table space, the use of the cutlery, toilets, general organisation, food and service. The waiter is doing a job for which they should be adequately paid- no 'optional' about it- so the menu price should include this.
So your delivery driver did the job for which you'd already paid, OP.
If it's really excellent service that goes above and beyond what you'd normally expect (IE, intact food at your front door delivered with basic politeness), then OK, a tip might be nice. But it shouldn't be expected as a given.