While using your demo store, I added a new product (Metafile Companion) in a new category (Software) with a price of $29 and discounts for quantity 2 at $21 and 10 at $16.
If I add 1 copy to the cart and then update it to 2 and press Update the Subtotal correctly reports $42.00, but the Total incorrectly says $58. If I press Update a second time, the Total is corrected.
I am looking to purchase a DNN store module, but this is a "show-stopper" for me. If there is a work-around or fix, please let me know. Thanks!