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	$38.35	5.363%	$40.4067	$40.41	$40.40	$40.40
Purchase #2	$60.32	3.600%	$62.4915	$62.49	$62.50	$62.50
Purchase #3	$121.99	6.667%	$130.1231	$130.12	$130.10	$130.10
Purchase #4	$126.37	12.327%	$141.9476	$141.95	$141.95	$141.90
Purchase #5	$143.70	4.106%	$149.6003	$149.60	$149.60	$149.60
Purchase #6	$95.81	13.345%	$108.5958	$108.60	$108.60	$108.60
Purchase #7	$132.83	13.847%	$151.223	$151.22	$151.20	$151.20
7 purchase totals =	$719.37		$784.3880	$784.39	$784.35	$784.30