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	$100.99	10.423%	$111.5162	$111.52	$111.50	$111.50
Purchase #2	$72.55	9.512%	$79.451	$79.45	$79.45	$79.50
Purchase #3	$94.51	5.313%	$99.5313	$99.53	$99.55	$99.50
Purchase #4	$52.98	12.575%	$59.6422	$59.64	$59.65	$59.60
Purchase #5	$247.59	5.217%	$260.5068	$260.51	$260.50	$260.50
Purchase #6	$52.29	4.610%	$54.7006	$54.70	$54.70	$54.70
Purchase #7	$65.61	3.119%	$67.6564	$67.66	$67.65	$67.70
7 purchase totals =	$686.52		$733.0045	$733.01	$733.00	$733.00