I just wanted coffee, not a math lesson

I stop by one of the many Dunkin Donuts near my school before trial team practice this morning. I need my pick me up plus my breakfast. This exact store is not my typical Dunkin where they know exactly what I want and don't even have to ask when I walk in the door. I made a colossal error in judgment by going to this store.

Me: I'll have an extra large coffee, cream sugar, and a chocolate chip muffin
Clerk: Ok [Fills coffee, hands it back to me]
Me: With cream and sugar please [Hands it back to her]
Clerk: Sorry about that. Would you like anything else?
Me: Yes, a chocolate chip muffin.

She grabs the muffin, puts it in a bag and hands it me. I hand her a ten dollar bill. The total for this should be $3.41. I get the same thing every day, so I know this routine quite well. She punches in the numbers and hands me my change.

Clerk: $2.15 is your change
Me: I handed you a ten

I have no idea how she got $2.15. $3.41 + $2.15 = $5.56. Somehow $4.44 disappeared into the nether. When I brought this to her attention, a puzzled look on her face takes over, looks at the change in my hand, reaches into the cash drawer, and hands me two singles. I hand everything back to her.

Me: The total should be $3.41. That means I should get $6.59 back.

The puzzled look returns to her face and she takes several seconds staring at the cash drawer. Eventually, she grabs a five, a one, and a handful of change and hands it to me.

Clerk: Math is not my strong suit.

I'm glad that they have you manning the register.