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	$226.31	3.762%	$234.8238	$234.82	$234.80	$234.80
Purchase #2	$21.65	13.313%	$24.5323	$24.53	$24.55	$24.50
Purchase #3	$208.35	7.766%	$224.5305	$224.53	$224.55	$224.50
Purchase #4	$221.46	13.689%	$251.7757	$251.78	$251.80	$251.80
Purchase #5	$78.54	5.383%	$82.7678	$82.77	$82.75	$82.80
Purchase #6	$186.55	4.397%	$194.7526	$194.75	$194.75	$194.80
Purchase #7	$62.41	5.117%	$65.6035	$65.60	$65.60	$65.60
7 purchase totals =	$1,005.27		$1,078.7862	$1,078.78	$1,078.80	$1,078.80