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	$26.77	11.617%	$29.8799	$29.88	$29.90	$29.90
Purchase #2	$75.48	10.130%	$83.1261	$83.13	$83.15	$83.10
Purchase #3	$162.31	4.149%	$169.0442	$169.04	$169.05	$169.00
Purchase #4	$116.59	12.698%	$131.3946	$131.39	$131.40	$131.40
Purchase #5	$172.58	11.110%	$191.7536	$191.75	$191.75	$191.80
Purchase #6	$96.40	8.367%	$104.4658	$104.47	$104.45	$104.50
Purchase #7	$105.50	5.211%	$110.9976	$111.00	$111.00	$111.00
7 purchase totals =	$755.63		$820.6618	$820.66	$820.70	$820.70