How to apply different Sales Tax rates to the same Membership Type - Back Office
You can do this with Price Sets. I'll document the entire set up:


Go to Administer -> CiviContribute -> CiviContribute Component Settings
and check the box Enable Tax &amp; Invoicing (Tax = Sales Tax; Invoicing you get as a bonus)
Go to Administer -> CiviContribute -> Financial Accounts 
and create one Financial Account for each Sales Tax Rate


Ignore Tax-Deductible - it is not related to Sales Tax; it potentially could be used to track whether monies are deductible for Income Tax purposes but I don't recommend it [there are other ways to track that; will document that at some point]. Click Is Tax -> (Tax = Sales Tax) and enter the Tax Rate right below it.



Repeat until you have the 3 Financial Accounts needed (3 different Sales Tax rates):




Set up Financial Types -> And associate each one with a one of the Financial Accounts we just created. Note we can add a 4th one [for out of Country residents] - i.e. with no Sales Tax.





Next are Price Sets - create a Price Set - for each Membership Type/Sales Tax Option - Yes that's a lot of Price Sets. Let's look at one: in the Maritime Provinces the Sales Tax is 15% -> so we need to create a Priceset that has a Line Item that hooks up to the Financial Type that has the 15% Tax Rate associated with it:




Looking at the Individual Price Fields:




Putting it all together - in Back Office -> from a Contact Summary record -> Membership tab -> Add Membership or Create Credit Card Membership




And selecting that Priceset results in the correct Amounts