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	$103.89	7.395%	$111.5727	$111.57	$111.55	$111.60
Purchase #2	$126.90	9.527%	$138.9898	$138.99	$139.00	$139.00
Purchase #3	$54.59	12.495%	$61.411	$61.41	$61.40	$61.40
Purchase #4	$79.73	5.117%	$83.8098	$83.81	$83.80	$83.80
Purchase #5	$63.90	8.579%	$69.382	$69.38	$69.40	$69.40
Purchase #6	$33.88	13.509%	$38.4568	$38.46	$38.45	$38.50
Purchase #7	$245.96	3.763%	$255.2155	$255.22	$255.20	$255.20
7 purchase totals =	$708.85		$758.8376	$758.84	$758.80	$758.90