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	$45.34	9.323%	$49.567	$49.57	$49.55	$49.60
Purchase #2	$127.69	12.263%	$143.3486	$143.35	$143.35	$143.30
Purchase #3	$17.25	3.371%	$17.8315	$17.83	$17.85	$17.80
Purchase #4	$39.49	3.580%	$40.9037	$40.90	$40.90	$40.90
Purchase #5	$22.43	12.270%	$25.1822	$25.18	$25.20	$25.20
Purchase #6	$233.86	9.242%	$255.4733	$255.47	$255.45	$255.50
Purchase #7	$140.41	8.146%	$151.8478	$151.85	$151.85	$151.80
7 purchase totals =	$626.47		$684.1541	$684.15	$684.15	$684.10