Warning: The Following Story Did Indeed Happen

It is true. We do need to worry about the state of the world. Especially if people like the the one in the following story will be in it.

After ordering a sandwich, I made way to the cash register to pay for it. The 'sandwich artist' slowly punched the buttons on the register and gave me the total. $7.28
I counted out .28 cents and gave it to her along with a ten dollar bill. Puzzled, she looks at the change in her hand and asks, "What is this? Is this a tip or something?"
Me, "Er, no. It's .28 cents. 'Cause it came to $7.28"
So with the .28 cents still cupped in one hand, she began to count out my change, $2.72.
Me, "It's going to be $3 change back to me."
Again confused, she looked up at me and then at the register's screen, "No, $2.72."
Me, "But I gave you $10.28. It came to $7.28, right?"
Holding the change in one hand, she picks up the ten, "We don't need the change. You gave me this" [indicating the ten].

It was at this point that I had to again try to explain that I gave her the 'extra' .28 cents to make it an even $10.28 so I could get three dollars back. I still don't think she understood, but she did slam three loonies into my hand.

How can someone be this clueless? I understand sometimes we forget things but it quickly comes back to us upon reminder. This was as though she's never even known about adding or subtracting. Scary.