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	$16.61	6.748%	$17.7308	$17.73	$17.75	$17.70
Purchase #2	$124.86	11.656%	$139.4137	$139.41	$139.40	$139.40
Purchase #3	$19.93	6.723%	$21.2699	$21.27	$21.25	$21.30
Purchase #4	$76.79	11.510%	$85.6285	$85.63	$85.65	$85.60
Purchase #5	$63.37	5.826%	$67.0619	$67.06	$67.05	$67.10
Purchase #6	$208.45	7.838%	$224.7883	$224.79	$224.80	$224.80
Purchase #7	$117.53	9.433%	$128.6166	$128.62	$128.60	$128.60
7 purchase totals =	$627.54		$684.5097	$684.51	$684.50	$684.50