https://help.tallysolutions.com/docs/te9rel60/Tax_India/VAT/BR_Override_value_and_rate.htm

Overriding Assessable Value and Tax Rate

You can configure VAT details to allow modification or overriding of the assessable value and tax rate in invoices.

To record transaction by overriding tax details

1.    Go to Gateway of Tally > Accounting Vouchers > F8: Sales.

2.    Click F12: Configure and set the options as given below:

o     Set Use common ledger account for item allocation? to No.

o     Set Allow modification of tax details for VAT? to Yes.

3.    Select the customer ledger in Party's A/c Name option.

4.    Select the required stock items whose VAT rates are specified either at the stock group level or at the stock item level. Enter Quantity and Rate for each stock item.

5.    Select a common sales ledger in which the option Is VAT/CST Applicable? is set to Applicable, and the option Set/Alter VAT Details? is not enabled in the Accounting Details screen.

o     Click F12: Configure in the VAT Classification Details screen and set the options as shown below:

o     Press Enter to return to the VAT Details screen.

o     Select the Classification/Nature in the VAT Details screen.

o     Enter the required Tax rate and Assessable Value. The VAT Details screen appears as shown below:

Note: The option Additional tax rate appears below the Tax rate field for Gujarat and Uttar Pradesh.

o     Press Enter to return to invoice.

6.    Select the common VAT ledger.

     The ledger must be grouped under Duties & Taxes in which the options:

o     Type of duty/tax set to VAT (CST in case of interstate sales).

o     Percentage of Calculation (eg 5)? set to 0.

The sales invoice appears as shown below:

7.    Press O to override the default tax details.