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	$204.46	8.261%	$221.3504	$221.35	$221.35	$221.40
Purchase #2	$214.34	5.363%	$225.8351	$225.84	$225.85	$225.80
Purchase #3	$90.25	10.125%	$99.3878	$99.39	$99.40	$99.40
Purchase #4	$106.94	3.831%	$111.0369	$111.04	$111.05	$111.00
Purchase #5	$63.61	10.708%	$70.4214	$70.42	$70.40	$70.40
Purchase #6	$132.27	6.213%	$140.4879	$140.49	$140.50	$140.50
Purchase #7	$192.47	4.859%	$201.8221	$201.82	$201.80	$201.80
7 purchase totals =	$1,004.34		$1,070.3416	$1,070.35	$1,070.35	$1,070.30