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	$52.75	6.859%	$56.3681	$56.37	$56.35	$56.40
Purchase #2	$70.60	9.319%	$77.1792	$77.18	$77.20	$77.20
Purchase #3	$36.68	7.637%	$39.4813	$39.48	$39.50	$39.50
Purchase #4	$111.68	5.389%	$117.6984	$117.70	$117.70	$117.70
Purchase #5	$231.38	10.710%	$256.1608	$256.16	$256.15	$256.20
Purchase #6	$159.98	10.206%	$176.3076	$176.31	$176.30	$176.30
Purchase #7	$229.64	11.174%	$255.3	$255.30	$255.30	$255.30
7 purchase totals =	$892.71		$978.4954	$978.50	$978.50	$978.60