You are expected to maintain bill books mandatorily by the I-T Dept. However, if you are a small-time trader with your annual turnover less than Rs.40 lakh, then you are permitted to declare your income on presumption at 5% of your actual sales. {U/s 44AF]. In that event no books of account need be maintained. Similarly, civil contractors don’t need to maintain books of account {u/s 44AD] in case 8% of the turnover is disclosed as profits. Transporters owning less than 10 goods carriage can also avail the benefit of presumptive income scheme without maintenance of books of account. However, if you declare your income below the minimum level/percentage provided under the scheme, you will necessarily have to maintain the books and get them audited.