With Square you can Create, Get, and List taxes with our APIs. You’ll use the Catalog API to UpsertCatalogObject to create the tax object with the type TAX. Once created you can ListCatalog with the type TAX. Lastly if you have that catalog_object_id for the tax you can retrieve it with RetrieveCatalogObject.
Additionally you can SearchCatalogObject to query for taxes as well. 