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	$25.75	9.328%	$28.152	$28.15	$28.15	$28.20
Purchase #2	$64.69	3.345%	$66.8539	$66.85	$66.85	$66.90
Purchase #3	$248.53	3.260%	$256.6321	$256.63	$256.65	$256.60
Purchase #4	$13.65	13.667%	$15.5155	$15.52	$15.50	$15.50
Purchase #5	$158.81	4.332%	$165.6896	$165.69	$165.70	$165.70
Purchase #6	$133.78	12.643%	$150.6938	$150.69	$150.70	$150.70
Purchase #7	$125.93	11.648%	$140.5983	$140.60	$140.60	$140.60
7 purchase totals =	$771.14		$824.1352	$824.13	$824.15	$824.20