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	$86.89	4.512%	$90.8105	$90.81	$90.80	$90.80
Purchase #2	$138.92	13.809%	$158.1035	$158.10	$158.10	$158.10
Purchase #3	$163.64	5.383%	$172.4487	$172.45	$172.45	$172.40
Purchase #4	$94.53	10.656%	$104.6031	$104.60	$104.60	$104.60
Purchase #5	$217.59	11.454%	$242.5128	$242.51	$242.50	$242.50
Purchase #6	$32.92	5.304%	$34.6661	$34.67	$34.65	$34.70
Purchase #7	$40.65	8.563%	$44.1309	$44.13	$44.15	$44.10
7 purchase totals =	$775.14		$847.2756	$847.27	$847.25	$847.20