two tipping questions i've had lately

1. how much do you tip when there's a delivery fee? say you order a pizza and it's $15 and there's a $2 delivery fee, how much do you tip?? $2 less than what you would have tipped or the same? does the driver get that fee or the business??

2. when having groceries delivered, how do you tip? per bag? a percentage of the total (that would be $$!!)? a set amount? by the number of trips the driver has to take bringing them in? (i've got a lot of stairs, so i feel like i should be generous, but you're already paying a delivery fee)

i'm good with most tips, but things involving answering the door are pretty new to me (i didn't have things delivered when i was home alone before)