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	$228.32	12.214%	$256.207	$256.21	$256.20	$256.20
Purchase #2	$143.82	7.398%	$154.4598	$154.46	$154.45	$154.50
Purchase #3	$217.42	11.816%	$243.1103	$243.11	$243.10	$243.10
Purchase #4	$143.81	10.279%	$158.5922	$158.59	$158.60	$158.60
Purchase #5	$96.49	3.772%	$100.1296	$100.13	$100.15	$100.10
Purchase #6	$226.62	10.639%	$250.7301	$250.73	$250.75	$250.70
Purchase #7	$222.92	11.249%	$247.9963	$248.00	$248.00	$248.00
7 purchase totals =	$1,279.40		$1,411.2253	$1,411.23	$1,411.25	$1,411.20