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	$148.49	12.381%	$166.8745	$166.87	$166.85	$166.90
Purchase #2	$103.60	4.675%	$108.4433	$108.44	$108.45	$108.40
Purchase #3	$63.98	3.866%	$66.4535	$66.45	$66.45	$66.50
Purchase #4	$136.78	10.385%	$150.9846	$150.98	$151.00	$151.00
Purchase #5	$104.85	6.771%	$111.9494	$111.95	$111.95	$111.90
Purchase #6	$141.73	3.809%	$147.1285	$147.13	$147.15	$147.10
Purchase #7	$80.69	8.766%	$87.7633	$87.76	$87.75	$87.80
7 purchase totals =	$780.12		$839.5971	$839.58	$839.60	$839.60