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	$19.42	6.556%	$20.6932	$20.69	$20.70	$20.70
Purchase #2	$227.42	12.625%	$256.1318	$256.13	$256.15	$256.10
Purchase #3	$244.98	3.509%	$253.5763	$253.58	$253.60	$253.60
Purchase #4	$153.65	12.409%	$172.7164	$172.72	$172.70	$172.70
Purchase #5	$207.75	10.145%	$228.8262	$228.83	$228.85	$228.80
Purchase #6	$207.31	10.462%	$228.9988	$229.00	$229.00	$229.00
Purchase #7	$240.90	11.593%	$268.8275	$268.83	$268.85	$268.80
7 purchase totals =	$1,301.43		$1,429.7702	$1,429.78	$1,429.85	$1,429.70