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	$43.43	12.512%	$48.864	$48.86	$48.85	$48.90
Purchase #2	$21.83	9.504%	$23.9047	$23.90	$23.90	$23.90
Purchase #3	$115.86	10.680%	$128.2338	$128.23	$128.25	$128.20
Purchase #4	$18.92	13.373%	$21.4502	$21.45	$21.45	$21.50
Purchase #5	$72.34	8.505%	$78.4925	$78.49	$78.50	$78.50
Purchase #6	$191.78	12.454%	$215.6643	$215.66	$215.65	$215.70
Purchase #7	$57.49	10.104%	$63.2988	$63.30	$63.30	$63.30
7 purchase totals =	$521.65		$579.9083	$579.89	$579.90	$580.00