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	$128.81	9.387%	$140.9014	$140.90	$140.90	$140.90
Purchase #2	$216.30	11.266%	$240.6684	$240.67	$240.65	$240.70
Purchase #3	$230.45	4.175%	$240.0713	$240.07	$240.05	$240.10
Purchase #4	$145.99	4.382%	$152.3873	$152.39	$152.40	$152.40
Purchase #5	$99.79	3.825%	$103.607	$103.61	$103.60	$103.60
Purchase #6	$231.65	10.848%	$256.7794	$256.78	$256.80	$256.80
Purchase #7	$71.78	9.617%	$78.6831	$78.68	$78.70	$78.70
7 purchase totals =	$1,124.77		$1,213.0979	$1,213.10	$1,213.10	$1,213.20