System -> Configuration -> Tax -> WebShopApps Tax On Shipping you will find the global settings for the Tax on Shipping extension.
|Highest tax rate in cart||The cart contents and their tax rates are examined. The highest tax rate in the cart is the tax rate used for shipping tax.|
|Lowest tax rate in cart||Exactly the opposite of above, the lowest tax rate in the cart is used to calculate tax on shipping.|
|Flat tax rate on taxable cart||Use this algorithm if you only are required to tax shipping when there are taxable items in the order. The shipping amount is taxed at a flat rate specified under Tax Classes in your tax configuration. Using this algorithm this flat rate of shipping tax is only applied if there are taxable items in the cart.|
|Highest value in the cart||The cart contents are examined and their tax rates. The value of items in the cart in each tax rate are compared and the tax rate of the group with the highest value is used as the shipping tax rate.|
|Weight proportion in cart||Each item in the cart’s proportional weight against the total cart weight is used to determine a proportion of the shipping and handling charges. The items’ tax rates are then applied to this value and these are totalled for all items in the cart.|