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	$132.59	12.768%	$149.5191	$149.52	$149.50	$149.50
Purchase #2	$7.96	8.287%	$8.6196	$8.62	$8.60	$8.60
Purchase #3	$101.62	9.676%	$111.4528	$111.45	$111.45	$111.50
Purchase #4	$37.35	8.359%	$40.4721	$40.47	$40.45	$40.50
Purchase #5	$26.31	11.462%	$29.3257	$29.33	$29.35	$29.30
Purchase #6	$178.76	4.646%	$187.0652	$187.07	$187.05	$187.10
Purchase #7	$141.42	7.138%	$151.5146	$151.51	$151.50	$151.50
7 purchase totals =	$626.01		$677.9691	$677.97	$677.90	$678.00