I worked 3 hours tonight and took 3 trips (2 doubles and a single). My 4th run was a credit card. The guy signed the slip and handed me a small wad of $1's. When I got to the car, I saw that he had put $5 on the credit card tip line and added it to the total. I thought I also had $5 in singles.
I thought about it for a couple seconds, then decided to phone him to make sure this was what he intended. $5 is a pretty generous tip in itself, and I didn't want to take advantage of him if this was a mistake. Much to my surprise, he confirmed that he intended to give me the $11 tip (I actually had $6 ones.
Totals for the night were 3 hours, 5 deliveries, 18 miles, and $22 in tips.