Lost in Translation

Lach and I just went for a walk over to the local Asian grocer to get a bit of a break from our full time job of stopping fraud. What started out as a harmless break turned into a post.
I consider myself to be pretty open-minded and try to be understanding of others. I don't expect everyone to have English as their first language - especially in the Internation District of Seattle, so this post is in no way a stab at other cultures. Before I get too far into my argument I guess I should set the scene.
I picked up 2 fuji apples and an Odwalla mo'beta shake. Lach had a salad and tea. I was first in line and as I was paying for my food I asked the cashier for cashback. a $5 and 5 $1's. The woman behind the counter nods and says, "yeah". Then proceeds to give me a $10. Now normally I'd let that slide but I needed the smaller change for a tip I intend to give later in the day. So I stop the woman before she starts ringing Lachlan up. I say, "I'm sorry, I asked for a $5 and 5 $1's."
Cashier: "oh, yeah." She then opens the register back up and gives me 2 $5!
Me: "Okay, I need $5 and 5 $1's."
Cashier: "oh, yeah." and then she counts to five on her fingers.
I nod in approval and watch as she opens the till back up and counts out 5 $1s.
By the time she gives me the correct change Lach has cashed out and we are finally able to leave. But I can't help feeling irritated. Not because she didn't understand me; I was more than happy to help her. It was that she acted like she was listening and wasn't. 2 TIMES!