Are you feeling pressured because the screen is right there in front of you? Don't be - for a basic coffee order at a café, a dollar or two is perfectly fine, or skip it entirely if you're on a tight budget. Those iPad screens are designed to make tipping feel obligatory, but most people aren't throwing down 20% for a latte they ordered themselves at the counter. If the barista actually did something special (made you a complicated drink, remembered your usual order), then 15-20% makes sense, but for a straightforward coffee, whatever feels comfortable to you is the right amount.