Need Some Changes in Codeigniter Project

I have POS system script. Right now in POS we need to use mouse. Because tab option not working fine for all options in POS. Now required work was need to make it works with tab options and also need to add dynamic order, like price vary based on quantity of product ordered. For example price for 1 kg was 100/- if quantity was 5Kg then price should be 490/- (2/- discount for each KG on ordering 5Kg and above) like that.