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	$240.57	9.239%	$262.7963	$262.80	$262.80	$262.80
Purchase #2	$63.57	4.610%	$66.5006	$66.50	$66.50	$66.50
Purchase #3	$103.67	8.208%	$112.1792	$112.18	$112.20	$112.20
Purchase #4	$95.89	8.729%	$104.2602	$104.26	$104.25	$104.30
Purchase #5	$19.49	12.580%	$21.9418	$21.94	$21.95	$21.90
Purchase #6	$164.71	6.145%	$174.8314	$174.83	$174.85	$174.80
Purchase #7	$233.25	9.581%	$255.5977	$255.60	$255.60	$255.60
7 purchase totals =	$921.15		$998.1072	$998.11	$998.15	$998.10