There is no need to produce an invoice for each job, but you are required to keep account of all your business related income, a daily cash book would suffice, also if you have a seperate bank account for the business and lodge all you income this will also be a back up. get and keep receipts for everything you buy for the business. at the end of the year compile all the figures and give to your accountant , or just hand the whole lot to him to sort out, but the more work they have to do the more they will charge