Spanish Misunderstanding

Here goes a typical Spanish transaction/interaction for me...I go into a bookstore to look around. I decide I want to buy a notebook. I go to the register to pay. On the back it says 40 euro cents, so I take it out to pay. I give the very cute Spanish guy my 40 cents and he says something about one. I think I need one more cent for tax or something, so I go digging in my bag for it. I finally hand him a 2 cent coin because i can't find a one cent coin. He is looking at me strangely until I realize he is saying that I've already paid and he has no idea what I am doing. I say yes in agreement and walk out, leaving behind my extra two cents, all the while realizing that there is no one cent coin anyways...if only I looked more foreign people would understand that I am only a clueless American!