At the bottom of the 'Locations' page, you'll find 'Tax Rates'.
Tax rates are ones you manually input to Hosted Solutions and get charged to Mobile App customers assigned to that location. If a location does not have a tax rate, tax will not be charged. If a customer is not assigned to a location, they will not be charged tax.
Customers get assigned to a location by being manually assigned, enrolling in a wash club at that location (kiosk sign up).