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	$177.34	7.629%	$190.8693	$190.87	$190.85	$190.90
Purchase #2	$226.74	12.613%	$255.3387	$255.34	$255.35	$255.30
Purchase #3	$5.40	9.617%	$5.9193	$5.92	$5.90	$5.90
Purchase #4	$36.52	4.241%	$38.0688	$38.07	$38.05	$38.10
Purchase #5	$34.87	7.466%	$37.4734	$37.47	$37.45	$37.50
Purchase #6	$126.77	10.192%	$139.6904	$139.69	$139.70	$139.70
Purchase #7	$214.88	3.275%	$221.9173	$221.92	$221.90	$221.90
7 purchase totals =	$822.52		$889.2772	$889.28	$889.20	$889.30