When a developer configures a tax integration for a store, the previously calculated tax entries during the checkout flow are deleted from the Cart. A tax integration is an integration that calculates and applies tax rates and amounts to a Cart or an Order based on various factors, such as product type, price, quantity, location, and tax rules. A tax integration can use either an external tax service provider or custom Apex code to perform the tax calculation. When a developer configures a tax integration for a store, any existing tax entries in the Cart are deleted before calling the tax integration service or method. This ensures that the tax calculation is accurate and up-to-date based on the current state of the Cart and avoids any conflicts or inconsistencies with previous tax entries. The previously calculated tax entriesare not ignored during recalculation, saved prior to recalculation, or modified with the new tax calculation, as these are not valid actions for handling existing tax entries. Salesforce References: B2B Commerce Developer Guide: Tax Integration, B2B Commerce Developer Guide: Tax Calculation Flow