Root has nothing to do with in-app purchases. It's like asking if you wash your windshield will you still be able to fill your tires.
Some apps won't run at all on a rooted phone, but there's an Xposed Installer module named RootCloak Module that can hide the fact that the phone is rooted from the apps you choose. (If the app asks for root privilege, RootCloak just returns with no response, which is what a non-rooted phone would do.) My TV app (the one for my cable company) runs just fine - except for root, and RootCloak makes it work just fine.