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	$61.46	8.716%	$66.8169	$66.82	$66.80	$66.80
Purchase #2	$132.95	13.167%	$150.4555	$150.46	$150.45	$150.50
Purchase #3	$15.72	8.426%	$17.0446	$17.04	$17.05	$17.00
Purchase #4	$42.56	13.147%	$48.1554	$48.16	$48.15	$48.20
Purchase #5	$122.99	3.554%	$127.3611	$127.36	$127.35	$127.40
Purchase #6	$172.97	10.574%	$191.2598	$191.26	$191.25	$191.30
Purchase #7	$29.85	12.462%	$33.5699	$33.57	$33.55	$33.60
7 purchase totals =	$578.50		$634.6632	$634.67	$634.60	$634.80