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	$210.86	8.302%	$228.3656	$228.37	$228.35	$228.40
Purchase #2	$155.88	9.630%	$170.8912	$170.89	$170.90	$170.90
Purchase #3	$9.40	12.866%	$10.6094	$10.61	$10.60	$10.60
Purchase #4	$92.30	7.521%	$99.2419	$99.24	$99.25	$99.20
Purchase #5	$205.65	10.734%	$227.7245	$227.72	$227.70	$227.70
Purchase #6	$94.72	4.770%	$99.2381	$99.24	$99.25	$99.20
Purchase #7	$92.55	12.468%	$104.0891	$104.09	$104.10	$104.10
7 purchase totals =	$861.36		$940.1598	$940.16	$940.15	$940.10