You’ve just finished a lunch with colleagues and the bill comes. You’re a finance guy—you know how to calculate a tip. But service today, well, it didn’t leave you smiling. Gratuity app may serve you well. Plug in the amount of the check, and click on the face that resembles how you feel—and the tip suggestion comes up with the total in place. Even better, you can split the bill by the number of people you lunched with—nice when everyone wants to expense on their own. You can also choose the kind of service you’re tipping: taxi, bar, restaurant and even a casino. But if you're actually in Vegas, and playing the odds, consider leaning more on the generous side. It's always safer to leave the house smiling.