So you earn a decent amount of money through tips? By tracking everything you earn, you are going to have an easier time maximizing your income. ServerLife for iPhone can help with that. It is a trip tracker that lets you track your daily to annual totals. It can track tips, hours, and notes.
The app can be configured to remind you to enter your tips. It breaks down your daily averages to help you make sense of your data. With an in-app purchase, you can unlock credit/cash tips, hourly wage, mileage, and other advanced features.
You can try this app for free but the premium version costs $2.99. More info is available here.