Yes. You can enable tracking Cash and Credit Card tips from the Settings Page. Enable tracking them by clicking on the selector next to "Track Cash and Credit Tips".
Once enabled the following will happen:
The fields Cash Tips and Credit Tips will show on the Tip Add and Tip Update pages.
These new values will added to calculate your Total Tips.
You'll see the values below each chart on the History and Average pages.
Your existing tips will still display the fields you entered when they were created. This is because the app does not know how to separate your total tips into Cash and Credit.