Levi's India — payment of extra tax

Address:

Jorhat, Assam, 785001

Today i purchased two items from levi's store (Ne real con). As said by shopkeeper that there is a 40% discount if you are buying 2 items. My total bill amount was rs.5798 after 40% discount the amount should be rs.3478 rupees but shopkeeper said your billing amount is rs.3896 when he was done the billing. When i asked why you have charged rupees 417 extra. He said it is gst.
But why separate gst on these items when already all type of taxes have been paid? And it is written on price tag also that (Inclusive all taxes).
Please clarify and do the needful.