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	$159.68	6.142%	$169.4875	$169.49	$169.50	$169.50
Purchase #2	$125.87	3.775%	$130.6216	$130.62	$130.60	$130.60
Purchase #3	$91.43	13.386%	$103.6688	$103.67	$103.65	$103.70
Purchase #4	$166.59	3.604%	$172.5939	$172.59	$172.60	$172.60
Purchase #5	$131.90	6.175%	$140.0448	$140.04	$140.05	$140.00
Purchase #6	$143.45	11.692%	$160.2222	$160.22	$160.20	$160.20
Purchase #7	$63.86	10.846%	$70.7863	$70.79	$70.80	$70.80
7 purchase totals =	$882.78		$947.4251	$947.42	$947.40	$947.40