I'm struggling to configure my Magento store to do the following with TAX.

I want to give a product a price which includes the tax amount specified i.e 20% so when I add it to the cart the TAX and grand total are displayed correctly.

For example:

My product has a price of £20. 20% TAX of £3.33 is built into the price. When this product is added to the cart I'd like the cart to display the TAX amount of £3.33 and the grand total of £20.

Right now all I can get is the grand total to add the TAX on top totalling £23.33. Also the display price is £23.33 not £20.

I'd love some help!