Historically, I've always tried to use the manned check out lines instead of the self check out to support the cashiers. However, seeing all these people wanting $15/hr to work in fast food really stuns me that people think they should be "entitled" to a living wage working the register in these kind of jobs. In my opinion, those jobs are for kids having no skills and needing spending money.
Now, what is really fun yet cruel to do is buy something for $15.53, hand them a twenty, wait till they punch it in, and then say, "Wait, I've got three cents". Amazing how it locks up their brains. Then again, I used to tutor math at the community college and the number of people I met who counted 21 + 4 on their fingers also stunned me.