You can define and charge taxes/fees on a service-by-service basis. This allows you the flexibility to set different taxes rates for different services, or have some services be tax-exempt.
How to add a tax to a service
From the Zenbooker admin page, go to Services, select or create a service, then under the Service Details section click Charge tax and enter the tax rate and tax name to apply to this service.
Then click Save for your changes to be applied.