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	$11.67	6.451%	$12.4228	$12.42	$12.40	$12.40
Purchase #2	$78.25	9.407%	$85.611	$85.61	$85.60	$85.60
Purchase #3	$154.37	4.594%	$161.4618	$161.46	$161.45	$161.50
Purchase #4	$141.80	3.734%	$147.0948	$147.09	$147.10	$147.10
Purchase #5	$250.69	8.591%	$272.2268	$272.23	$272.25	$272.20
Purchase #6	$62.85	11.828%	$70.2839	$70.28	$70.30	$70.30
Purchase #7	$91.47	9.160%	$99.8487	$99.85	$99.85	$99.80
7 purchase totals =	$791.10		$848.9498	$848.94	$848.95	$848.90