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	$105.53	5.324%	$111.1484	$111.15	$111.15	$111.10
Purchase #2	$229.80	7.582%	$247.2234	$247.22	$247.20	$247.20
Purchase #3	$237.65	8.344%	$257.4795	$257.48	$257.50	$257.50
Purchase #4	$192.72	12.280%	$216.386	$216.39	$216.40	$216.40
Purchase #5	$103.29	5.338%	$108.8036	$108.80	$108.80	$108.80
Purchase #6	$191.87	10.111%	$211.27	$211.27	$211.25	$211.30
Purchase #7	$119.82	6.570%	$127.6922	$127.69	$127.70	$127.70
7 purchase totals =	$1,180.68		$1,280.0031	$1,280.00	$1,280.00	$1,280.00