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	$139.56	10.496%	$154.2082	$154.21	$154.20	$154.20
Purchase #2	$196.89	13.170%	$222.8204	$222.82	$222.80	$222.80
Purchase #3	$11.83	5.714%	$12.506	$12.51	$12.50	$12.50
Purchase #4	$245.82	7.854%	$265.1267	$265.13	$265.15	$265.10
Purchase #5	$149.96	12.863%	$169.2494	$169.25	$169.25	$169.20
Purchase #6	$161.75	6.466%	$172.2088	$172.21	$172.20	$172.20
Purchase #7	$131.33	7.737%	$141.491	$141.49	$141.50	$141.50
7 purchase totals =	$1,037.14		$1,137.6105	$1,137.62	$1,137.60	$1,137.50