You can change the tax percentage which is automatically suggested when you issue a new invoice.
Change taxes on an invoice
Open either a created invoice, or create a new one.
Enter customer information.
On the new invoice, choose a customer.
Add an item and mark the item taxable in the Invoice Details area.
To change the tax rate you can pick another one from pre-entered values by clicking the arrow next to the tax rate.
On the Tax Rates page, choose another tax and click OK on the upper right of the page.
See Add a new tax rate with Microsoft Invoicing if you need to add a new rate to the list.
Send or preview the invoice.