Automatic gst rate

Automatic gst rates should be applied when generating an invoice through already saved hsn codes. I own a garments store. When I create an invoice I have to manually change gst rate if my item price goes above 2500 because gst rate on items below 2500 is 5 % and above 2500 is 18%. Same should apply to discounted items like when I sell something for 2400 having mrp 2600 it should apply 5% not 18%