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	$18.44	13.162%	$20.8671	$20.87	$20.85	$20.90
Purchase #2	$70.61	11.576%	$78.7838	$78.78	$78.80	$78.80
Purchase #3	$48.58	6.472%	$51.7241	$51.72	$51.70	$51.70
Purchase #4	$197.84	7.592%	$212.86	$212.86	$212.85	$212.90
Purchase #5	$81.65	12.580%	$91.9216	$91.92	$91.90	$91.90
Purchase #6	$146.45	8.635%	$159.096	$159.10	$159.10	$159.10
Purchase #7	$131.44	10.509%	$145.253	$145.25	$145.25	$145.30
7 purchase totals =	$695.01		$760.5056	$760.50	$760.45	$760.60