Tipping inflation is real, and it’s coming to a tablet near you.

Merchants using Square SQ, -0.43% and other mobile payment services can set “recommended” tip amounts or percentages for any transaction — including ones that traditionally haven’t included tips. Your payment card is swiped through a device attached to an iPad or other tablet, and you’re presented with a screen suggesting you add a gratuity.

People have reported being prompted for sizable tips at bakeries, food trucks and takeout counters. Hop in a New York City cab, and the credit card reader will prompt you to leave a 20%, 25% or 30% tip. Get a haircut or a massage, and you may be presented with a screen that has the “25% tip” box already checked.

Square cautions businesses against setting suggested tip amounts too high, saying that “can alienate customers and make it less likely that they’ll come back.” But Square also recommends merchants add a “no tip” option precisely because a survey found some people were more likely to leave a gratuity this way.

“It’s one thing to bypass a tip jar or just leave the gratuity line blank when you’re signing a check, but it’s harder to physically press a button saying you aren’t going to leave anything,” the company tells merchants.

Many people feel added pressure because the would-be recipient is standing right there, watching the transaction. Even in restaurants, where customers used to leave a cash tip or a signed credit card receipt on the table, waiters may be swiping cards at the diners’ elbows and presenting them with “add a tip” screens.

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Tipping rules haven’t changed, regardless of what a merchant’s screen is telling you, says etiquette expert Lizzie Post, co-president of the Emily Post Institute and co-host of the “Awesome Etiquette” podcast. Fifteen to 20% is still the accepted range for taxi rides, haircuts, spa services and table service in sit-down restaurants.

“You can tip with confidence. You have no obligation to tip more,” Post says.

Gratuities are important in full-service restaurants, since servers often are paid less than the federal minimum wage on the assumption they will earn tips. Restaurant tips are traditionally based on the pretax amount of the bill, although some merchants are guilty of suggesting tips based on the total bill. People may default to 20% because the math is easier, or opt to base the tip on the after-tax bill, but that’s all discretionary, Post says.

There’s also no obligation to leave a tip for a takeout order, unless it was complicated or included curbside delivery. In that case, 10% is fine. Home delivery merits a 10 to 15% tip, with pizza delivery meriting a $2 to $5 tip. In most other situations, tip screens can be viewed just like tip jars — entirely optional.

What if you want to leave a tip, just not what the screen is suggesting? You can leave cash, of course, but you’ll typically have the option to change or customize a gratuity that’s charged to your card.

“I feel no shame in completely ignoring it, hitting ‘other option’ and putting in my percentage that I feel comfortable using,” Post says. “It is your discretion what you put there.”

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