Sesami itself doesn't handle payments directly of your bookings, but instead is using the Shopify foundation and framework.
Good news though, Shopify has recently released new tipping features. Please refer to the official Shopify help pages to learn how to set it up on your account:
- https://help.shopify.com/en/manual/checkout-settings/tips
- https://help.shopify.com/en/manual/sell-in-person/pos-classic/transactions/tips