Set both of the Small/Medium and the Large Tare Rates to 0:0 ...

In the Modules ... Shipping ... install the Per Unit perweightunit shipping module ...

Now, go to your Products and set the shipping charge for the Products in the Product Weight ... so if you want to charge 2.99 for a Product, then set the Product Weight to 2.99 ...

Now, that Product will ship for 2.99 x quantity in the cart with the Per Unit perunitweight shipping module ...