/accounting mode
Ideally, you wouldn't have to pay taxes on an item twice assuming it is sales tax. Sales tax is the tax you pay on retrieval of the item. While you do get double taxed in MANY situations (state tax AND federal tax levels), these are applied to income tax not sales. The issue at hand is that I believe Joe is facing a canadian custom imports tariff, which is a tax in it's own right, but is more correctly coined as a tariff (a cost for bringing items into the country).
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The jist of custom tariffs. I'm not 100% on canadian law, but that's basically it. This is a tax for bringing items not made in canada, into canada.
Edit: What ronith said too.