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	$145.49	10.307%	$160.4857	$160.49	$160.50	$160.50
Purchase #2	$139.31	6.316%	$148.1088	$148.11	$148.10	$148.10
Purchase #3	$126.43	11.815%	$141.3677	$141.37	$141.35	$141.40
Purchase #4	$17.96	4.513%	$18.7705	$18.77	$18.75	$18.80
Purchase #5	$110.62	12.386%	$124.3214	$124.32	$124.30	$124.30
Purchase #6	$38.65	5.411%	$40.7414	$40.74	$40.75	$40.70
Purchase #7	$29.33	10.231%	$32.3308	$32.33	$32.35	$32.30
7 purchase totals =	$607.79		$666.1263	$666.13	$666.10	$666.10