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	$207.77	6.676%	$221.6407	$221.64	$221.65	$221.60
Purchase #2	$137.32	6.536%	$146.2952	$146.30	$146.30	$146.30
Purchase #3	$154.78	4.208%	$161.2931	$161.29	$161.30	$161.30
Purchase #4	$133.86	11.235%	$148.8992	$148.90	$148.90	$148.90
Purchase #5	$117.68	8.640%	$127.8476	$127.85	$127.85	$127.80
Purchase #6	$62.49	6.354%	$66.4606	$66.46	$66.45	$66.50
Purchase #7	$247.59	8.727%	$269.1972	$269.20	$269.20	$269.20
7 purchase totals =	$1,061.49		$1,141.6336	$1,141.64	$1,141.65	$1,141.60