Enabling tax by line item will allow you to mark each item individually in the proposal as taxable or non-taxable.

To enable this setting, navigate to Settings > Proposal Settings > Proposal Settings in your Floranext dashboard.

Find the Tax by Line section and set Tax by Line to Yes and click Save in the upper right.

Now when you open a proposal, for each item you can find a check box next to the item to mark it as taxable or not.