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	$30.65	9.662%	$33.6114	$33.61	$33.60	$33.60
Purchase #2	$177.94	6.526%	$189.5524	$189.55	$189.55	$189.60
Purchase #3	$11.98	10.687%	$13.2603	$13.26	$13.25	$13.30
Purchase #4	$137.84	7.848%	$148.6577	$148.66	$148.65	$148.70
Purchase #5	$196.76	9.162%	$214.7872	$214.79	$214.80	$214.80
Purchase #6	$99.42	12.263%	$111.6119	$111.61	$111.60	$111.60
Purchase #7	$150.88	11.353%	$168.0094	$168.01	$168.00	$168.00
7 purchase totals =	$805.47		$879.4903	$879.49	$879.45	$879.60