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	$127.63	13.314%	$144.6227	$144.62	$144.60	$144.60
Purchase #2	$39.43	6.312%	$41.9188	$41.92	$41.90	$41.90
Purchase #3	$41.92	8.309%	$45.4031	$45.40	$45.40	$45.40
Purchase #4	$84.39	12.834%	$95.2206	$95.22	$95.20	$95.20
Purchase #5	$38.75	3.105%	$39.9532	$39.95	$39.95	$40.00
Purchase #6	$206.49	11.800%	$230.8558	$230.86	$230.85	$230.90
Purchase #7	$154.51	4.812%	$161.945	$161.95	$161.95	$161.90
7 purchase totals =	$693.12		$759.9192	$759.92	$759.85	$759.90