I always carry cash and in this situation, as @Empireapple says, if it was raining anywhere near as hard there as it was here a few days ago, I’d have tipped $5. But the way he handled it was inappropriate and especially to do this to a female was just wrong. I would also have asked for a receipt, perhaps have reiterated that I was authorizing only a $5 charge, and as @BunsenBurner said, not have worried about the valve caps. Then I’d have gone home, called the cr card company and disputed the charge. The gas station would have been notified and they would have to address it with the employee or eat the charge (most cr card companies would simply credit your account for a small amount like that).
Now on the flip side, when someone does something nice for me, I always put a positive review on their website or email their customer service company or ask to speak to a manager. Have done this with several online orders I placed, supermarket, theater and drugstore staff, etc. A little kindness goes a long way.