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	$15.26	10.387%	$16.8451	$16.85	$16.85	$16.80
Purchase #2	$95.98	4.627%	$100.421	$100.42	$100.40	$100.40
Purchase #3	$202.40	11.534%	$225.7448	$225.74	$225.75	$225.70
Purchase #4	$80.78	9.462%	$88.4234	$88.42	$88.40	$88.40
Purchase #5	$151.31	13.733%	$172.0894	$172.09	$172.10	$172.10
Purchase #6	$89.93	5.109%	$94.5245	$94.52	$94.50	$94.50
Purchase #7	$166.32	11.642%	$185.683	$185.68	$185.70	$185.70
7 purchase totals =	$801.98		$883.7312	$883.72	$883.70	$883.60