Restaurant girls - I haven't sorted out the money yet

The girl at the checkout of the works restaurant thinks I'm everso simple. She noticed the buldging wallet full of coins as I neglected to give her the right money for my lunch. So, now the routine is that I get all the coins out and she shows me which ones I need to pay for my lunch.

The problem is a size and value one. The 5c coin is bigger than the 10c coin - how confusing!

I should mention that the staff in the works restaurant are fantastic, some are even English! And that the food is really great and really cheap. For less than I pay for a bread roll from the vending machine at work, I get a fresh made sandwich and starbucks coffee to go with it!