I updated your _JSON file to pass back the RowDiscount that you need on line 24. Save a backup of that file since you will have to add it again if you make changes to the cart in the future.
I also updated your total column so that the span had the id attribute and not the div so that the remove link wouldn't be replaced after update.
The total is off because you have accounted for the discount in the TotalPrice column. You basically either need a discount rule or to account for it in the TotalPrice. By doing it both places the discount is doubled.
I didn't correct this because there are a couple of ways you might want it to work