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	$52.53	13.255%	$59.4929	$59.49	$59.50	$59.50
Purchase #2	$122.49	9.818%	$134.5161	$134.52	$134.50	$134.50
Purchase #3	$170.97	8.644%	$185.7486	$185.75	$185.75	$185.70
Purchase #4	$225.94	11.455%	$251.8214	$251.82	$251.80	$251.80
Purchase #5	$46.82	8.783%	$50.9322	$50.93	$50.95	$50.90
Purchase #6	$143.42	5.661%	$151.539	$151.54	$151.55	$151.50
Purchase #7	$50.95	8.222%	$55.1391	$55.14	$55.15	$55.10
7 purchase totals =	$813.12		$889.1893	$889.19	$889.20	$889.00