The SubTotal and No Tax SubTotal column header in Order Totals report is renamed to Taxable Subtotal and Nontaxable Subtotal respectively.
The Nontaxable Subtotal will include items that have no tax associated with them. From below transaction, it will be the subtotal of the items highlighted in yellow.
The Taxable Subtotal will include the items that have tax associated with them, like the item highlighted in pink.
Order Totals report can be opened from Report > Sales Order report group.
Reference: Task 772