To override tax in checkout, a developer must implement the sfdc_checkout.TaxCalculations interface. The sfdc_checkout.TaxCalculations interface is an Apex interface that provides methods for customizing the tax calculation logic for a cart or an order. The interface allows the developer to define how to retrieve tax rates and rules, how to apply tax amounts and adjustments, and how to handle tax errors and exceptions. The developer can use the sfdc_checkout.TaxCalculations interface to integrate with a third-party tax service provider or to implement their own tax calculation logic. The other interfaces do not exist or are not related to tax calculation. Salesforce Reference:B2B Commerce Developer Guide: Tax Integration,B2B Commerce Developer Guide: Tax Calculations Interface