Conflicted

So, today at school today I was given the opportunity to play "crime-fighter"... I was hungry, so I stopped in the campus cafeteria and bought a Starbucks Frapaccino and a breakfast sandwich. I went to the cashier and she rang up my total as $5.16 or so... But as I handed her the cash, she voided one of my items and the total dropped down to $2.00 and some odd change. This was a big red flag to me, as I worked ten years in food service. Five as a waiter in a restaurant, and five in the kitchen and cafeteria at Sacred Heart Medical Center. As I walked away, I kept an eye on the cashier, and she pocketed the extra two dollars from the voided item...
Yeah, so after eating my sandwich, I decided it was the right thing to inform the kitchen manager. I asked for the manager, and told him of the situation. He went ahead and checked the sales records on the computer in the back... I don't know the outcome of the situation, but I felt really conflicted because of it.

On one hand, I really dislike theft. Honesty is a big virtue in my book. It really bothers me to see my cash that is meant to pay for the food, as well as pay for my college experience, end up in the pocket of a cashier. It disgusts me to no end.
But on the other hand, I really feel bad about putting the cashier's job, integrity, and college education in jeopardy. A lot is at stake here, but I have to keep telling myself that I essentially didn't put her in that situation; she did it on her own.