ASP.NET and JQuery - Correction and new functions

In tax; IVA=16%, IEPS=8%, one posibility: IVA + IEPS , second IVA, 3er posibility 0% tax. four posibility, 4posibility only IEPS tax When try to add new product and exist in shopping cart display message and add cant with new cant. No duplicate products in same order. Search of product for code (clave) or search for description Allway Focus in product input text for search , permit use of scaner. Posibility apply dicount on global total, discount on all products in the order. This annull individual discount on all products. Permit select the payment type, cash or credit card, if credit card make a charge of 2.5% frame rigth