Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$15.56	9.102%	$16.9763	$16.98	$17.00	$17.00
Purchase #2	$36.42	4.831%	$38.1795	$38.18	$38.20	$38.20
Purchase #3	$126.38	3.776%	$131.1521	$131.15	$131.15	$131.20
Purchase #4	$200.56	13.344%	$227.3227	$227.32	$227.30	$227.30
Purchase #5	$212.72	13.266%	$240.9394	$240.94	$240.95	$240.90
Purchase #6	$74.92	4.822%	$78.5326	$78.53	$78.55	$78.50
Purchase #7	$163.26	10.184%	$179.8864	$179.89	$179.90	$179.90
7 purchase totals =	$829.82		$912.9890	$912.99	$913.05	$913.00