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	$121.89	8.206%	$131.8923	$131.89	$131.90	$131.90
Purchase #2	$66.70	9.763%	$73.2119	$73.21	$73.20	$73.20
Purchase #3	$58.40	6.342%	$62.1037	$62.10	$62.10	$62.10
Purchase #4	$20.58	9.176%	$22.4684	$22.47	$22.45	$22.50
Purchase #5	$44.52	5.348%	$46.9009	$46.90	$46.90	$46.90
Purchase #6	$72.71	6.522%	$77.4521	$77.45	$77.45	$77.50
Purchase #7	$194.64	5.256%	$204.8703	$204.87	$204.85	$204.90
7 purchase totals =	$579.44		$618.8996	$618.89	$618.85	$619.00