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	$204.90	8.109%	$221.5153	$221.52	$221.50	$221.50
Purchase #2	$111.85	8.754%	$121.6413	$121.64	$121.65	$121.60
Purchase #3	$55.36	8.185%	$59.8912	$59.89	$59.90	$59.90
Purchase #4	$155.48	3.729%	$161.2778	$161.28	$161.30	$161.30
Purchase #5	$24.72	11.144%	$27.4748	$27.47	$27.45	$27.50
Purchase #6	$208.55	8.349%	$225.9618	$225.96	$225.95	$226.00
Purchase #7	$79.91	12.567%	$89.9523	$89.95	$89.95	$90.00
7 purchase totals =	$840.77		$907.7145	$907.71	$907.70	$907.80