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	$64.53	3.626%	$66.8699	$66.87	$66.85	$66.90
Purchase #2	$151.91	13.336%	$172.1687	$172.17	$172.15	$172.20
Purchase #3	$90.91	13.381%	$103.0747	$103.07	$103.05	$103.10
Purchase #4	$229.92	11.668%	$256.7471	$256.75	$256.75	$256.70
Purchase #5	$32.36	5.203%	$34.0437	$34.04	$34.05	$34.00
Purchase #6	$40.85	4.269%	$42.5939	$42.59	$42.60	$42.60
Purchase #7	$121.76	8.737%	$132.3982	$132.40	$132.40	$132.40
7 purchase totals =	$732.24		$807.8962	$807.89	$807.85	$807.90