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	$61.88	7.829%	$66.7246	$66.72	$66.70	$66.70
Purchase #2	$141.83	11.731%	$158.4681	$158.47	$158.45	$158.50
Purchase #3	$202.42	6.504%	$215.5854	$215.59	$215.60	$215.60
Purchase #4	$100.76	13.816%	$114.681	$114.68	$114.70	$114.70
Purchase #5	$148.47	11.763%	$165.9345	$165.93	$165.95	$165.90
Purchase #6	$52.82	5.715%	$55.8387	$55.84	$55.85	$55.80
Purchase #7	$144.61	13.122%	$163.5857	$163.59	$163.60	$163.60
7 purchase totals =	$852.79		$940.8180	$940.82	$940.85	$940.80