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	$71.83	13.288%	$81.3748	$81.37	$81.35	$81.40
Purchase #2	$15.59	13.177%	$17.6443	$17.64	$17.65	$17.60
Purchase #3	$104.46	3.710%	$108.3355	$108.34	$108.35	$108.30
Purchase #4	$99.83	11.603%	$111.4133	$111.41	$111.40	$111.40
Purchase #5	$103.84	8.311%	$112.4701	$112.47	$112.45	$112.50
Purchase #6	$66.97	4.714%	$70.127	$70.13	$70.15	$70.10
Purchase #7	$75.63	8.758%	$82.2537	$82.25	$82.25	$82.30
7 purchase totals =	$538.15		$583.6187	$583.61	$583.60	$583.60