Step 1: Update Sales Tax Rates for Future Transactions
Go to Setups > Accounting and Payroll > Sales Tax Rates
Highlight the tax rate you want to change and click Edit
Make your changes and click OK to save
This updates the tax rate for all future Repair Orders (ROs) and Part invoices you create
Step 2: Recalculate Sales Tax on Open/Unpaid ROs and Part Invoices
Open each open or unpaid Repair Order or Part Invoice
Click the Miscellaneous blue link on the left
At the top left of that window, below Service Writer (or Part Counter), locate Tax Code
Click Select, choose the updated tax code, and click OK
This will recalculate the sales tax for that specific RO or Part Invoice
Repeat this for each open Repair Order and Part Invoice to apply the updated tax rates