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NEW YORK - On-demand apps make life easier: A few taps on my phone and I can get a cab in minutes or groceries delivered to my door.

The hard part? Figuring how much -- or if -- I should tip the people who drive me around or pick out my cheese at the supermarket.

Part of the confusion arises from the companies themselves. Some don't allow tipping through their apps, even though they say tipping is allowed. And the policies posted on their websites can be unclear.

Just like other service professionals, we should tip these types of workers, says Sharon Schweitzer, etiquette consultant and founder of Protocol & Etiquette Worldwide. Many of them have to reach into their own pockets to pay for gas, bike repairs or other costs, and a tip can help them make ends meet, Schweitzer says.

"The apps are designed for us to evolve to a cashless society," she says, "however that doesn't mean we become heartless in the process."

Indeed, cash is best if you have it. Some companies, like FreshDirect, will deduct processing fees that credit card companies charge before paying the driver, so they won't get the full amount of your tip.

Click ahead for some tipping suggestions from etiquette experts.