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	$85.85	9.279%	$93.816	$93.82	$93.80	$93.80
Purchase #2	$74.58	13.533%	$84.6729	$84.67	$84.65	$84.70
Purchase #3	$158.58	4.188%	$165.2213	$165.22	$165.20	$165.20
Purchase #4	$94.31	9.760%	$103.5147	$103.51	$103.50	$103.50
Purchase #5	$107.73	3.342%	$111.3303	$111.33	$111.35	$111.30
Purchase #6	$129.32	11.472%	$144.1556	$144.16	$144.15	$144.20
Purchase #7	$98.47	6.238%	$104.6126	$104.61	$104.60	$104.60
7 purchase totals =	$748.84		$807.3234	$807.32	$807.25	$807.30