You can design your cart however you please. plum.Shop has a series of special short codes that you can use to define where you want product details to appear in the item list. You can use the built-in Google Checkout and PayPal methods, or you can define a custom checkout method.
In this demo, tax rates are defined according to New York laws. If the subtotal is over $55, the rate is 4.5%. Under $55, there is no tax.
It is also set to have free shipping with an order over $200.