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	$128.84	6.703%	$137.4761	$137.48	$137.50	$137.50
Purchase #2	$142.62	5.627%	$150.6452	$150.65	$150.65	$150.60
Purchase #3	$50.99	8.352%	$55.2487	$55.25	$55.25	$55.20
Purchase #4	$242.54	7.832%	$261.5357	$261.54	$261.55	$261.50
Purchase #5	$59.82	4.641%	$62.5962	$62.60	$62.60	$62.60
Purchase #6	$139.58	7.214%	$149.6493	$149.65	$149.65	$149.60
Purchase #7	$105.52	5.766%	$111.6043	$111.60	$111.60	$111.60
7 purchase totals =	$869.91		$928.7555	$928.77	$928.80	$928.60