With this small amount of income it is doubtful you need to make quarterly payments. Have you filed returns in past years? If you were due a refund that expected refund will offset any tax due. Need to owe $1000 in taxes annually to make quarterly payments. There is a work sheet on form 1040 es http://www.irs.gov/pub/irs-pdf/f1040es.pdf
that is helpful. Really should report all your self employment income. Chances are minimal you'd ever be caught if you don't have a business checking account. Bank reports deposits to IRS.