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	$225.51	10.813%	$249.8944	$249.89	$249.90	$249.90
Purchase #2	$221.79	7.596%	$238.6372	$238.64	$238.65	$238.60
Purchase #3	$109.74	5.848%	$116.1576	$116.16	$116.15	$116.20
Purchase #4	$198.77	9.528%	$217.7088	$217.71	$217.70	$217.70
Purchase #5	$48.58	8.857%	$52.8827	$52.88	$52.90	$52.90
Purchase #6	$57.87	13.222%	$65.5216	$65.52	$65.50	$65.50
Purchase #7	$157.52	12.189%	$176.7201	$176.72	$176.70	$176.70
7 purchase totals =	$1,019.78		$1,117.5224	$1,117.52	$1,117.50	$1,117.50