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	$53.45	3.865%	$55.5158	$55.52	$55.50	$55.50
Purchase #2	$200.50	12.528%	$225.6186	$225.62	$225.60	$225.60
Purchase #3	$87.50	9.189%	$95.5404	$95.54	$95.55	$95.50
Purchase #4	$173.31	4.132%	$180.4712	$180.47	$180.45	$180.50
Purchase #5	$112.85	5.288%	$118.8175	$118.82	$118.80	$118.80
Purchase #6	$71.85	3.594%	$74.4323	$74.43	$74.45	$74.40
Purchase #7	$20.42	6.230%	$21.6922	$21.69	$21.70	$21.70
7 purchase totals =	$719.88		$772.0880	$772.09	$772.05	$772.00