The Taxes module is integrated with Conditional Actions to provide extreme flexibility in the way tax rules are set up. For each tax rule defined in Ubercart, a set of Conditional Actions conditions may be applied to it which control whether the tax is applied to an order.
Define the Tax Rates
Configuring taxes is a two-step process. First the taxes and their rates are defined on the Tax Settings page under Store administration > Configuration. Under the list of taxes is a link to "Make a new tax rule." The form it brings up allows you to specify the name and rate of the tax, as well as the product and line item types it applies to. Because it's possible for taxes to apply to tax amounts, the weights of the tax rules may be important. Taxes are only ever applied to lighter taxes.
Add Workflow Conditions
Once the tax rules are set up, head over to the Conditional Actions page under Site configuration. You should see a row for each of the tax rules (plus the configurations from other modules). By clicking edit, you can access the conditions and actions that are evaluated whenever Ubercart calculates the taxes. If the conditions return true for an order, the tax in the action is calculated and applied to it. See the Conditional Actions Configuration page for more information.