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	$70.83	6.702%	$75.577	$75.58	$75.60	$75.60
Purchase #2	$157.53	12.168%	$176.6983	$176.70	$176.70	$176.70
Purchase #3	$165.35	8.156%	$178.8359	$178.84	$178.85	$178.80
Purchase #4	$83.38	7.245%	$89.4209	$89.42	$89.40	$89.40
Purchase #5	$78.47	8.826%	$85.3958	$85.40	$85.40	$85.40
Purchase #6	$68.99	11.404%	$76.8576	$76.86	$76.85	$76.90
Purchase #7	$89.71	11.725%	$100.2285	$100.23	$100.25	$100.20
7 purchase totals =	$714.26		$783.0140	$783.03	$783.05	$783.00