Tax Callback Class provides you the mechanism to communicate with a Tax Engine of your choice for tax calculation on invoice generation. You need to provide details like Invoice Line Item or a Credit Memo Line Item, Handback, Tax Address, Tax Code, and Taxable Amount to the callback. You must register the Tax Callback Class in Config Custom Classes in Custom Setting.
For more information, see Tax Callback Class. You can find information about how to setup the callback, method description, the working of the callback, and sample code in that topic.