Create new taxCRM gives you the ability to add unlimited tax rates on your invoices/estimates/proposals etc..
- Navigate to Setup->Finance->Tax Rates.
- Click on the top left button New Tax
- Enter tax name
- Enter tax rate
- Click Save
Hide tax per item
When updating tax and this tax is already applied on item the tax information wont be changed.
If you are using your own templates for generating PDF for estimates and invoices you should not remove this logic from the templates if you want this option to work as it should, otherwise you can adjust the template to fit to your needs no matter how Show TAX per item option is set.