I think the closest solution to your problem that magento can offer is 1. set price in admin including tax which means the price you enter while creating the product is price including tax. To do this Goto System->Configuration page. Click on the Tax section and under the "Calculation Settings" tab, set "catalog price " to "Including tax". Now price entered for the products are assumed to be including tax.
In the same tax setting page, set the "Display Product Prices In Catalog" as "Including tax".
Now set up tax rates and rules as your requirement in Sales->Tax -> Tax rules and Tax rates pages.
And there you have it. Product prices in catalog listing will show product including tax, ie $100 And when you add product to cart. The cart will show
Subtotal = $100
Tax = $xx
Grand Total = $100