Hi there, I have had a number of customers ask for our invoices to read TAX INVOICE not just INVOICE. How do i change this on our invoices we send out? thank you

Howdy, mick-a-talbot.  

I'd be happy to help you in setting up sales tax to your invoices. Here's how: 

1. Click Taxes on the left pane. 
2. Select Set up tax. 
3. Set up the necessary details ,then select Next. 
4. Press Save.

Feel free to check out this handy article for details: Set up and use automated GST in QuickBooks Online.  

Additionally, I'm including an article an overview of using this feature: Applying Sales Tax to Transactions and Sales Forms. This resource provides steps for turning sales tax on and setting up tax items. 

If there's anything else you need help with, please don't hesitate to swing by anytime. Have a great day!