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	$62.39	6.580%	$66.4953	$66.50	$66.50	$66.50
Purchase #2	$129.53	13.231%	$146.6681	$146.67	$146.65	$146.70
Purchase #3	$100.84	12.597%	$113.5428	$113.54	$113.55	$113.50
Purchase #4	$207.45	11.809%	$231.9478	$231.95	$231.95	$231.90
Purchase #5	$205.51	9.770%	$225.5883	$225.59	$225.60	$225.60
Purchase #6	$151.89	4.235%	$158.3225	$158.32	$158.30	$158.30
Purchase #7	$120.65	8.376%	$130.7556	$130.76	$130.75	$130.80
7 purchase totals =	$978.26		$1,073.3204	$1,073.33	$1,073.30	$1,073.30