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	$107.83	3.647%	$111.7626	$111.76	$111.75	$111.80
Purchase #2	$58.31	5.143%	$61.3089	$61.31	$61.30	$61.30
Purchase #3	$77.52	4.503%	$81.0107	$81.01	$81.00	$81.00
Purchase #4	$49.83	9.528%	$54.5778	$54.58	$54.60	$54.60
Purchase #5	$9.83	5.538%	$10.3744	$10.37	$10.35	$10.40
Purchase #6	$237.63	6.785%	$253.7532	$253.75	$253.75	$253.80
Purchase #7	$17.42	9.509%	$19.0765	$19.08	$19.10	$19.10
7 purchase totals =	$558.37		$591.8641	$591.86	$591.85	$592.00