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	$247.27	11.359%	$275.3574	$275.36	$275.35	$275.40
Purchase #2	$56.28	4.291%	$58.695	$58.70	$58.70	$58.70
Purchase #3	$247.74	12.668%	$279.1237	$279.12	$279.10	$279.10
Purchase #4	$99.37	12.591%	$111.8817	$111.88	$111.90	$111.90
Purchase #5	$125.74	9.624%	$137.8412	$137.84	$137.85	$137.80
Purchase #6	$89.28	3.437%	$92.3486	$92.35	$92.35	$92.30
Purchase #7	$170.52	12.157%	$191.2501	$191.25	$191.25	$191.30
7 purchase totals =	$1,036.20		$1,146.4977	$1,146.50	$1,146.50	$1,146.50