Yes. You can enable the app to track your Sales Totals from the Settings Page. Enable tracking them by clicking on the selector next to "Track Sales Totals".

This will also enable the app to show you your Tip percentage %. This is the average % of tips that you received for that period. You may have some great tips and some not so great tips. Shoot for 20% average and you'll do well.

Increase your Sales Total and your and your earnings should follow.