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	$87.42	3.647%	$90.6082	$90.61	$90.60	$90.60
Purchase #2	$236.62	6.812%	$252.7386	$252.74	$252.75	$252.70
Purchase #3	$9.97	9.504%	$10.9175	$10.92	$10.90	$10.90
Purchase #4	$115.92	6.763%	$123.7597	$123.76	$123.75	$123.80
Purchase #5	$131.86	13.358%	$149.4739	$149.47	$149.45	$149.50
Purchase #6	$100.95	10.319%	$111.367	$111.37	$111.35	$111.40
Purchase #7	$176.87	7.622%	$190.351	$190.35	$190.35	$190.40
7 purchase totals =	$859.61		$929.2159	$929.22	$929.15	$929.30