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	$247.93	4.290%	$258.5662	$258.57	$258.55	$258.60
Purchase #2	$187.51	12.395%	$210.7519	$210.75	$210.75	$210.80
Purchase #3	$46.69	10.722%	$51.6961	$51.70	$51.70	$51.70
Purchase #4	$42.65	5.737%	$45.0968	$45.10	$45.10	$45.10
Purchase #5	$209.64	7.749%	$225.885	$225.89	$225.90	$225.90
Purchase #6	$28.36	13.637%	$32.2275	$32.23	$32.25	$32.20
Purchase #7	$105.45	10.485%	$116.5064	$116.51	$116.50	$116.50
7 purchase totals =	$868.23		$940.7299	$940.75	$940.75	$940.80