In case you want to alter the assessable value and tax rate in invoice, allow modification of tax details in F12: configure.
To record transaction by overriding tax details
1. Go to Gateway of Tally > Accounting Vouchers > F8: Sales.
2. Click F12: Configure to configure the sales invoice for overriding tax details.
o Set Use common ledger A/c for item allocation? to No.
o Set Allow modification of Tax Details for VAT? to Yes.
o Press Ctrl+A to accept the screen.
3. Select the party ledger in Party's A/c Name option.
4. Select the required stock items whose VAT rates are specified either at the stock group or stock item level. Enter Quantity and Rate for each stock item.
o Select a common sales ledger in which the option Is VAT/CST Applicable? is set to Applicable, and Set/Alter VAT Details? is disabled in the Accounting Details screen.
o Click F12: Configure in VAT Classification Details screen to configure override of tax rate.
o Select the Classification/Nature in VAT Details screen.
o Enter the required Tax rate. The VAT Details screen appears as shown below:
o Press Enter to return to invoice.
5. Select the common VAT ledger.
The sales invoice appears as shown below:
6. Press O to override the default tax details and save invoice with the changed tax rate.