For instance, a company say M/s First Source Ltd, which deals in buying and selling of second hand cars, purchases a second hand Maruti Celerio Car of March, 2014 make (Original price Rs. 5 lakh) for Rs. 3 lakhs from an unregistered person and sells the same after minor furbishing in July, 2017 for Rs. 3,50,000/-. The supply of the car to the company for Rs. 3 lakh shall be exempted and the supply of the same by the company to its customer for Rs. 3.5 lakh shall be taxed and GST shall be levied. The value for GST purpose shall be Rs. 50000/-, i.e. the difference between the selling and the purchase price of the company. Tally
In Tally, it can be done
Go to Sales voucher. Press F12 : Configure, Set "Yes" for the option "Allow modification of tax details for GST". By doing this in the voucher, it prompt the user to edit Taxable value as per your requirement. For example, in Sales voucher, the value may be 3,50,000/-. Howerver, one can override the Taxable value. In this case it has to be overridden with 50,000/- and tax will get calculated accordingly.
Also you can take printout of the invoice by disabling the GST Analysis using Print F12: Configuration