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	8.204%	$17.1287	$17.13	$17.15	$17.10
Purchase #2	$136.52	6.708%	$145.6778	$145.68	$145.70	$145.70
Purchase #3	$104.59	13.274%	$118.4733	$118.47	$118.45	$118.50
Purchase #4	$77.56	11.540%	$86.5104	$86.51	$86.50	$86.50
Purchase #5	$238.58	8.142%	$258.0052	$258.01	$258.00	$258.00
Purchase #6	$170.27	4.804%	$178.4498	$178.45	$178.45	$178.40
Purchase #7	$142.67	11.126%	$158.5435	$158.54	$158.55	$158.50
7 purchase totals =	$886.02		$962.7887	$962.79	$962.80	$962.70