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	$108.96	8.572%	$118.3001	$118.30	$118.30	$118.30
Purchase #2	$241.45	12.606%	$271.8872	$271.89	$271.90	$271.90
Purchase #3	$89.47	12.551%	$100.6994	$100.70	$100.70	$100.70
Purchase #4	$10.47	9.611%	$11.4763	$11.48	$11.50	$11.50
Purchase #5	$187.32	12.144%	$210.0681	$210.07	$210.05	$210.10
Purchase #6	$68.64	8.304%	$74.3399	$74.34	$74.35	$74.30
Purchase #7	$97.32	8.634%	$105.7226	$105.72	$105.70	$105.70
7 purchase totals =	$803.63		$892.4936	$892.50	$892.50	$892.50