In 1.12 there is a new check box under the Payment Options screen which will allow your customers to sign their receipt and select a tip percentage at the same time, hopefully giving a better experience for your customers and servers.
1. Select the Payment Options from the Payments section of the Toast Restaurant Admin page.
2. Select the combine tip and signature screen option under credit card section.
3. This is new tip dialog screen. The customer can select a percentage but they cannot move on until they tap the confirm payment button. After clicking confirm payment the receipt screen will ask the customer how they would like their receipt.
For more functionality, you can ask your customers to leave your restaurant feedback.