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	$100.76	3.678%	$104.466	$104.47	$104.45	$104.50
Purchase #2	$161.60	3.859%	$167.8361	$167.84	$167.85	$167.80
Purchase #3	$70.61	10.284%	$77.8715	$77.87	$77.85	$77.90
Purchase #4	$102.78	8.402%	$111.4156	$111.42	$111.40	$111.40
Purchase #5	$165.52	12.248%	$185.7929	$185.79	$185.80	$185.80
Purchase #6	$157.83	11.296%	$175.6585	$175.66	$175.65	$175.70
Purchase #7	$221.40	13.592%	$251.4927	$251.49	$251.50	$251.50
7 purchase totals =	$980.50		$1,074.5333	$1,074.54	$1,074.50	$1,074.60