Penny for Your Thoughts

Should you always be asked if you want your change back?  When you are paying for something and you get a few cents worth of change back, should you be asked if you want your few pennies or little bit of change back?

I'm just asking, because I paid for something this weekend and there was only a little change left out of the ten dollar bill I used, and the cashier, instead of asking if I wanted the few pennies back, just closed the register and went about his business.

I am not trying to get into any discussion about the amount of change.

Like OMG get over it, it was only a few pennies.

That is not the purpose of my asking.

I simply want to know if it is polite to ask or should it just be assumed that you don't get the few pennies back?