How to Add Tax to Paypal IPN Checkout

I've tried adding the "tax" field, however nothing tax related shows up in my checkout. How do I add the tax amount to my chec开发者_如何学Gokout for Paypal?

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I'm guessing you found an answer by now, but for the sake of the other people finding this question through Google:

If you're trying to add tax to a shopping cart, the variable name changes from "tax" to "tax_cart", as so (for 8% tax):

<input type="hidden" name="tax_cart" value="<?php echo number_format(($price * 0.08),2); ?>">