Sales Tax API

Manage sales tax on invoices and credit memos:

• POST /invoices/{id}/taxes - Add sales tax to an invoice
• PUT /invoices/{id}/taxes - Update sales tax on an invoice
• POST /invoices/{id}/calculate-tax - Calculate tax for an invoice
• POST /credit-memos/{id}/taxes - Add sales tax to a credit memo
• PUT /credit-memos/{id}/taxes - Update sales tax on a credit memo