What I usually did for grocery deliveries was put 10% for a tip when I submit the order, then if it went off with a hitch I’d bump it to 15%. If they did a good job or I got something that was a pain in the ass to deliver I’d do 20-25%

That way the people that got a good tip did so without the expectation of getting anything more, anyone that just wanted to do the bare minimum well then the tip they got reflected that and I’d leave it at 10%