When tipping extends to the self-checkout machine, who receives them?

Gone are the days when customers tipped a waitress who served them by putting cash directly in her hand. Now, point-of-sale kiosks prompt people for tips — even if the customer didn't interact with a human. 

The problem with tipping at a self-checkout machine is there's no proof the money goes to an employee, Wall Street Journal reporter Rachel Wolfe told CBS News. 

"Machines don't have the same protections as tipping human employees, so while the law requires that something called a "tip" has to go to employees, when you're tipping a machine, you can't be quite so sure," Wolfe said.