Hell yes I want my nickel

One afternoon a couple of months ago I visited a Mexican dining establishment that I frequent. I ordered my number 3 (grilled stuffed burrito, stale chips with processed cheese-like substance and a carbon based beverage) and was given a total of four dollars and ninety-five cents. Adding to the uniqueness of this situation, I, for some reason, had cash. I pulled up to the window and a young woman, wearing a purple uniform repeated the total. I gave her the five dollars and she thanked my as the currency exchanged hands. She stepped slightly away from the window to insert the money into the register and then looked back at me and asked, "Did you want your change?" I was almost sure that there was no way that she just asked me if I wanted my change so I said, "I'm sorry, what?"
"Do you want your change," there was no mistaking it this time. This girl wanted to steal my .05. I didn't know what to say. For a moment I thought, just let her have it, because she has already brought up the idea that no one would want a nickel change; just let her hang on to it. Rationality caught a hold of me in that moment and even though it took me a moment to reply, I replied, "uhm.....ya, I want my change." The young employee then explained that most people, when the amount of change is so low just tell her to keep it. She explained this as she placed the nickel in my palm with a forced smile. I felt like Scrooge, but I had my nickel.
This story brought about a few topics to discuss and I may not discuss them entirely here, just some food for thought.
1. What is the line that she makes in between when to ask if the person wants their change and when to just hand them their damned change like she should be doing in the first place?
2. If she asks every person if they want their change, how much is she supplementing her income?
2a. She makes minimum wage, so it's possible that this is a significant percentage of her income, possibly and additional 20%-25%.
3. How much change would you give up?

Personally. If the total were $4.99 and she asked me if I wanted my change, I would have looked at her like she was crazy and had the same response I did previously, "Hell yes I want my nickel."
(I can't seem to add the pictures I want at work, so I will have them on this evening)