Currently Customer Tax Address as set in system > settings > checkout ques off the customer address as selected by the Admin to use with customer billing or shipping address for the tax location and most often at least in US is the shipping address.
This works okay for most taxsing requirements, except in one case:
If Pickup from Store is selected - this changes the tax rules for an order as it now has to conform to the store location rules. This will probably be different than a customer billing or shipping address.
Please consider adding an option for Pickup from Store to allow Admin to use store address for location lookup or some way to refer to a "store" tax class that can be selected for the Pickup from Store that overrides the system > settings > checkout rules for all other taxation rules.
Thanks for considering this function.
Lee