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	$112.39	9.823%	$123.4301	$123.43	$123.45	$123.40
Purchase #2	$223.48	12.533%	$251.4887	$251.49	$251.50	$251.50
Purchase #3	$160.68	12.304%	$180.4501	$180.45	$180.45	$180.50
Purchase #4	$154.31	8.314%	$167.1393	$167.14	$167.15	$167.10
Purchase #5	$59.25	9.146%	$64.669	$64.67	$64.65	$64.70
Purchase #6	$59.53	5.373%	$62.7285	$62.73	$62.75	$62.70
Purchase #7	$140.53	7.563%	$151.1583	$151.16	$151.15	$151.20
7 purchase totals =	$910.17		$1,001.0640	$1,001.07	$1,001.10	$1,001.10