As per valuation provisions
Sec 15
(2) The value of supply shall include:-
....
.....(c) Incidental expenses , including commission and packing, charged by the supplier to the recipient of the supply and any amount charged for anything done by the supplier in respect of the supply of goods or services or both at the time of, or before delivery of goods or supply of services
In my opinion as per the above clause you will have to charge tax as applicable to your main supply as a composite supply.. For example if you are supplying 5 percent goods, tax shall be 5%. If you are selling exempt goods it will also be exempt.