A lot of stores won’t let the cashiers keep the change and if they do, they could be fired. Might not want to do that again.

Cashier's aren't allowed to keep the change. That would be considered stealing

So then you got to teach her how to receive good deeds/small gifts from customers. Well done!

That is tipping. Most businesses that do not have tipped employees are not set up to report tips, which is required by tax law. And businesses that do have tipped employees usually do not consider cashiers as a tipped employee, which means that they are not be paid at a tipped employee wage.

That's super awkward. Hopefully there was a donation jar or something the could toss it into.

I don't see the problem. Somebody had to be her first customer; turned out it was you.

That's just Gen Z losing their shit over trivial matters. All she had to do was calculate the difference, take it out of the till, and just give to someone else. It's not the end of the world. Relax. lol