if the name of the session variable is "tax" the calculation would be:
([Price] - ([Price] * $_SESSION['tax'])) * [Quantity]
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.