GST is fixed at 12% for branded goods above, 1000 Rs. and 5% for below 1000 Rs.
The rate of 1000 is selling price (MRP).
So if MRP of garment is 1299, tax rate will be 12%. But to be charged on value of supply. So you have to charge 12% on 700.
Again there is no MRP concept and only selling price concept. So if MRP is 1099, tax should be at 12%.