You can define a tax rule to always show tax in the cart and use math on the page to calculate and display a tax on the add to cart page if necessary.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.