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	$246.64	12.492%	$277.4503	$277.45	$277.45	$277.50
Purchase #2	$241.52	8.704%	$262.5419	$262.54	$262.55	$262.50
Purchase #3	$65.50	5.869%	$69.3442	$69.34	$69.35	$69.30
Purchase #4	$155.29	11.117%	$172.5536	$172.55	$172.55	$172.60
Purchase #5	$225.90	7.517%	$242.8809	$242.88	$242.90	$242.90
Purchase #6	$59.60	5.646%	$62.965	$62.97	$62.95	$63.00
Purchase #7	$9.54	13.301%	$10.8089	$10.81	$10.80	$10.80
7 purchase totals =	$1,003.99		$1,098.5448	$1,098.54	$1,098.55	$1,098.60