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	$120.92	8.400%	$131.0773	$131.08	$131.10	$131.10
Purchase #2	$112.87	9.273%	$123.3364	$123.34	$123.35	$123.30
Purchase #3	$140.46	12.147%	$157.5217	$157.52	$157.50	$157.50
Purchase #4	$175.51	8.639%	$190.6723	$190.67	$190.65	$190.70
Purchase #5	$137.45	12.448%	$154.5598	$154.56	$154.55	$154.60
Purchase #6	$234.37	12.151%	$262.8483	$262.85	$262.85	$262.80
Purchase #7	$114.53	12.266%	$128.5782	$128.58	$128.60	$128.60
7 purchase totals =	$1,036.11		$1,148.5940	$1,148.60	$1,148.60	$1,148.60