How to disable automatic round off in tally 9 for sales entr

If you are talking about tax rounding off, check Tax ledger master and change rounding off method. Accounts Info>ledger> alter> select ledger.

If you are talking about rounding of gross amount of sale bill, go to Accounts info>Voucher type>selct voucher type and check if Voucher class is activated. If voucher class is activated, rounding off method option could be changed from Class (last option on right hand side in Vaoucher Type alteration).

same problem

you have to put decimal places while creating unit of measurement