Atleast the books mentioned below are to be maintained (this is as per Rule 6F).
(i) a cash book;
(ii) a journal, if the accounts are maintained according to the mercantile system of accounting;
(iii) a ledger;
[(iv) carbon copies of bills, whether machine numbered or otherwise serially numbered, wherever such bills are issued by the person, and carbon copies or counterfoils of machine numbered or otherwise serially numbered receipts issued by him:
Provided that nothing in this clause shall apply in relation to sums not exceeding twenty-five rupees;]
(v) original bills wherever issued to the person and receipts in respect of expenditure incurred by the person or, where such bills and receipts are not issued and the expenditure incurred does not exceed fifty rupees, payment vouchers prepared and signed by the person: