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	$248.83	11.810%	$278.2168	$278.22	$278.20	$278.20
Purchase #2	$120.71	3.120%	$124.4762	$124.48	$124.50	$124.50
Purchase #3	$18.84	12.179%	$21.1345	$21.13	$21.15	$21.10
Purchase #4	$231.55	10.415%	$255.6659	$255.67	$255.65	$255.70
Purchase #5	$71.43	10.519%	$78.9437	$78.94	$78.95	$78.90
Purchase #6	$103.51	4.705%	$108.3801	$108.38	$108.40	$108.40
Purchase #7	$80.65	5.505%	$85.0898	$85.09	$85.10	$85.10
7 purchase totals =	$875.52		$951.9070	$951.91	$951.95	$951.90