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	$212.72	4.368%	$222.0116	$222.01	$222.00	$222.00
Purchase #2	$158.69	6.194%	$168.5193	$168.52	$168.50	$168.50
Purchase #3	$57.60	10.685%	$63.7546	$63.75	$63.75	$63.80
Purchase #4	$242.35	13.475%	$275.0067	$275.01	$275.00	$275.00
Purchase #5	$34.96	13.226%	$39.5838	$39.58	$39.60	$39.60
Purchase #6	$8.43	8.202%	$9.1214	$9.12	$9.10	$9.10
Purchase #7	$127.89	12.222%	$143.5207	$143.52	$143.50	$143.50
7 purchase totals =	$842.64		$921.5181	$921.51	$921.45	$921.50