Tapping her fingers isn't treating you like a dog. When people call you, you expect them to have their policy number ready, so why can't she expect you to have your money ready?
Idk about anyone else, but I try to pull out my wallet while I'm waiting in line behind other cars, and I keep loose change right in the console so I have easy access to it if I need it. If there are no cars in front of me but there are some behind me, I try to get it out while I'm placing my order. If there are no cars behind me, I won't even pull away from the speaker until I have the exact change in my hand, or my card or whatever.
The point is, there's plenty of time to sort yourself out before you get to the window.