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	$77.76	5.774%	$82.2499	$82.25	$82.25	$82.20
Purchase #2	$136.66	13.714%	$155.4016	$155.40	$155.40	$155.40
Purchase #3	$177.99	4.109%	$185.3036	$185.30	$185.30	$185.30
Purchase #4	$11.95	6.422%	$12.7174	$12.72	$12.70	$12.70
Purchase #5	$145.56	13.634%	$165.4057	$165.41	$165.40	$165.40
Purchase #6	$128.71	12.540%	$144.8502	$144.85	$144.85	$144.90
Purchase #7	$84.76	3.361%	$87.6088	$87.61	$87.60	$87.60
7 purchase totals =	$763.39		$833.5372	$833.54	$833.50	$833.50