TUCSON, Ariz. - From the teenager who made your sandwich at the deli, to your local coffee shop barista, more and more service providers might expect something a little extra, but does that mean you must pay up? In a recent Consumer Reports survey of more than 1,000 American adults, 27% said there are more situations today where they're expected to tip than there were just two years ago.

"Consumers are becoming increasingly resentful about the idea that they have to tip people just for doing their jobs. Like really? I have to tip a smoothie maker? Or what about the barista at the coffee shop who swivels a little point of sale iPad in your direction with a pre-calculated tip," says Consumer Reports Money Editor, Margot Gilman.

As for how much to tip, Consumer Reports has some guidelines.

"A simple rule of thumb is to tip 15-20% of the pre-tax restaurant tab. Don't tip less than 15%. If the server was rude or offensive, speak to the manager but don't stiff the server," says Gilman.

Another finding from CR's survey on tipping: 46% of Americans say they favor a system that would do away with tipping altogether and instead charge higher prices, a remedy promoted by restaurateur Danny Meyer, the founder of Shake Shack.

If you're looking for some tools to help, apps such as Tab, Settle Up, and Plates let you split tabs or keep track of who owes what.

Click here to see CR's complete list of recommended service providers to tip, and the amount.