In the upper left of the order screen, there is a Totals dropdown for the current order. By default, it shows the totals for the entire order.
There is a button on the bottom right of the dropdown that lets you switch between the whole order view and the totals for highlighted lines. As you select or deselect line, these totals will change.
The dropdown goes away when your mouse leaves the Totals area. If you want the totals to stay visible, click the Pin button and the dropdown will flip horizontally and stick until you click Unpin.
