I am working on a UK fashion store. The customer has a specific requirement - never add tax (VAT) at checkout; rather, have VAT built into the price, and deduct when applicable.

The use case is that EU purchases will have no tax added at checkout - as the price includes it. And, rest of the world purchases will have the VAT deducted at the checkout.

I can't see how to do this in Magento. I though to set up some negative values for tax rates, but that doesn't work.

Any ideas?