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	$250.52	13.698%	$284.8362	$284.84	$284.85	$284.80
Purchase #2	$143.38	11.139%	$159.3511	$159.35	$159.35	$159.40
Purchase #3	$226.53	6.433%	$241.1027	$241.10	$241.10	$241.10
Purchase #4	$230.60	3.418%	$238.4819	$238.48	$238.50	$238.50
Purchase #5	$103.67	4.753%	$108.5974	$108.60	$108.60	$108.60
Purchase #6	$136.76	10.829%	$151.5697	$151.57	$151.55	$151.60
Purchase #7	$226.42	12.740%	$255.2659	$255.27	$255.25	$255.30
7 purchase totals =	$1,317.88		$1,439.2049	$1,439.21	$1,439.20	$1,439.30