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	$15.83	6.411%	$16.8449	$16.84	$16.85	$16.80
Purchase #2	$101.25	4.341%	$105.6453	$105.65	$105.65	$105.60
Purchase #3	$102.48	8.745%	$111.4419	$111.44	$111.45	$111.40
Purchase #4	$179.27	6.734%	$191.342	$191.34	$191.35	$191.30
Purchase #5	$75.71	9.397%	$82.8245	$82.82	$82.80	$82.80
Purchase #6	$216.60	3.313%	$223.776	$223.78	$223.80	$223.80
Purchase #7	$10.89	13.573%	$12.3681	$12.37	$12.35	$12.40
7 purchase totals =	$702.03		$744.2427	$744.24	$744.25	$744.10