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	$14.46	3.707%	$14.996	$15.00	$15.00	$15.00
Purchase #2	$85.83	4.639%	$89.8117	$89.81	$89.80	$89.80
Purchase #3	$83.92	13.283%	$95.0671	$95.07	$95.05	$95.10
Purchase #4	$154.31	10.702%	$170.8243	$170.82	$170.80	$170.80
Purchase #5	$107.37	8.487%	$116.4825	$116.48	$116.50	$116.50
Purchase #6	$143.89	12.647%	$162.0878	$162.09	$162.10	$162.10
Purchase #7	$102.46	4.260%	$106.8248	$106.82	$106.80	$106.80
7 purchase totals =	$692.24		$756.0942	$756.09	$756.05	$756.10