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	$88.38	7.286%	$94.8194	$94.82	$94.80	$94.80
Purchase #2	$172.66	10.176%	$190.2299	$190.23	$190.25	$190.20
Purchase #3	$131.76	4.325%	$137.4586	$137.46	$137.45	$137.50
Purchase #4	$224.75	10.866%	$249.1713	$249.17	$249.15	$249.20
Purchase #5	$126.60	10.786%	$140.2551	$140.26	$140.25	$140.30
Purchase #6	$196.25	11.728%	$219.2662	$219.27	$219.25	$219.30
Purchase #7	$227.64	13.553%	$258.492	$258.49	$258.50	$258.50
7 purchase totals =	$1,168.04		$1,289.6925	$1,289.70	$1,289.65	$1,289.80