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	$185.75	8.117%	$200.8273	$200.83	$200.85	$200.80
Purchase #2	$145.84	13.447%	$165.4511	$165.45	$165.45	$165.50
Purchase #3	$108.68	11.563%	$121.2467	$121.25	$121.25	$121.20
Purchase #4	$94.78	9.349%	$103.641	$103.64	$103.65	$103.60
Purchase #5	$99.67	12.304%	$111.9334	$111.93	$111.95	$111.90
Purchase #6	$80.77	12.362%	$90.7548	$90.75	$90.75	$90.80
Purchase #7	$129.34	13.308%	$146.5526	$146.55	$146.55	$146.60
7 purchase totals =	$844.83		$940.4069	$940.40	$940.45	$940.40