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	$225.37	13.812%	$256.4981	$256.50	$256.50	$256.50
Purchase #2	$177.29	12.271%	$199.0453	$199.05	$199.05	$199.00
Purchase #3	$34.51	8.661%	$37.4989	$37.50	$37.50	$37.50
Purchase #4	$211.48	5.402%	$222.9041	$222.90	$222.90	$222.90
Purchase #5	$179.30	8.727%	$194.9475	$194.95	$194.95	$194.90
Purchase #6	$26.71	13.326%	$30.2694	$30.27	$30.25	$30.30
Purchase #7	$52.43	9.612%	$57.4696	$57.47	$57.45	$57.50
7 purchase totals =	$907.09		$998.6329	$998.64	$998.60	$998.60