Hi there aboveandbeyondto,
It's important that all information is filled out so that your transactions can be completed. QuickBooks Online is a great tool that allows you to create invoices for your customers and send them from the same software. I can provide some information about taxes on transactions in QuickBooks Online.
QuickBooks Online has the capability to have multiple tax rates per transaction for different items. That being said, as stated by PrachiJoshi, a tax code needs to be applied for every line of the transaction or it cannot be saved.
If you have any other questions, feel free to reach out here.
