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	$55.76	7.345%	$59.8556	$59.86	$59.85	$59.90
Purchase #2	$151.56	7.603%	$163.0831	$163.08	$163.10	$163.10
Purchase #3	$148.36	6.430%	$157.8995	$157.90	$157.90	$157.90
Purchase #4	$116.95	12.209%	$131.2284	$131.23	$131.25	$131.20
Purchase #5	$16.28	12.528%	$18.3196	$18.32	$18.30	$18.30
Purchase #6	$200.75	10.844%	$222.5193	$222.52	$222.50	$222.50
Purchase #7	$138.84	11.194%	$154.3817	$154.38	$154.40	$154.40
7 purchase totals =	$828.50		$907.2872	$907.29	$907.30	$907.30