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	$90.78	11.864%	$101.5501	$101.55	$101.55	$101.60
Purchase #2	$158.99	12.462%	$178.8033	$178.80	$178.80	$178.80
Purchase #3	$60.63	3.184%	$62.5605	$62.56	$62.55	$62.60
Purchase #4	$94.43	5.432%	$99.5594	$99.56	$99.55	$99.60
Purchase #5	$143.51	10.344%	$158.3547	$158.35	$158.35	$158.40
Purchase #6	$57.36	5.733%	$60.6484	$60.65	$60.65	$60.60
Purchase #7	$136.48	5.518%	$144.011	$144.01	$144.00	$144.00
7 purchase totals =	$742.18		$805.4874	$805.48	$805.45	$805.60