This option allows you to calculate two or more sales tax items expressed as a single item. This means the group of sales tax items is expressed as a single number on your line item grid when you select this item from the drop down list. Keep in mind this list can't be altered within the line item grid, for example, an invoice, so it's a good idea to create sales tax group items for specific customers or orders that require multiple tax items applied to them.
To add this as an item, you will need to add a new item within the Items app, and choose Sales Tax.
If you do not see the Items app, you will need to get access permission for this app from your administrator. The Items app is found in the Accounting Lists Pack.
Because you’re using this item to group sales tax items together, there is a List at the bottom of the screen that details which sales tax items are included. So the individual items are displayed here, and on your main items list, the group (containing these individual items) will be displayed as a single record.