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	$10.49	4.229%	$10.9336	$10.93	$10.95	$10.90
Purchase #2	$100.48	7.744%	$108.2612	$108.26	$108.25	$108.30
Purchase #3	$22.62	4.363%	$23.6069	$23.61	$23.60	$23.60
Purchase #4	$90.78	5.482%	$95.7566	$95.76	$95.75	$95.80
Purchase #5	$241.77	6.126%	$256.5808	$256.58	$256.60	$256.60
Purchase #6	$227.41	12.523%	$255.8886	$255.89	$255.90	$255.90
Purchase #7	$95.35	13.268%	$108.001	$108.00	$108.00	$108.00
7 purchase totals =	$788.90		$859.0287	$859.03	$859.05	$859.10