We need to provide a static tax rate for customer's selecting a specific method (Local Pickup). This tax rate would not be based on a customer zone and would supersede any zone rates that may exist.
I am able to obtain the shipping method from the order and also create a new TaxRate object but am unsure how to hook into the system to force this tax rate when the shipping method is selected.
I've tried returning the TaxRate object from a custom TaxResolver (extended from TaxRateResolverInterface) but it does not set a tax rate for the customer.
Any ideas as to how/where to force this tax rate to be applied?