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	$104.51	7.536%	$112.3859	$112.39	$112.40	$112.40
Purchase #2	$45.81	3.738%	$47.5224	$47.52	$47.50	$47.50
Purchase #3	$151.39	4.565%	$158.301	$158.30	$158.30	$158.30
Purchase #4	$215.57	12.197%	$241.8631	$241.86	$241.85	$241.90
Purchase #5	$83.47	8.827%	$90.8379	$90.84	$90.85	$90.80
Purchase #6	$50.69	4.491%	$52.9665	$52.97	$52.95	$53.00
Purchase #7	$88.45	12.806%	$99.7769	$99.78	$99.80	$99.80
7 purchase totals =	$739.89		$803.6537	$803.66	$803.65	$803.70