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	$44.46	4.657%	$46.5305	$46.53	$46.55	$46.50
Purchase #2	$207.71	9.491%	$227.4238	$227.42	$227.40	$227.40
Purchase #3	$97.89	13.759%	$111.3587	$111.36	$111.35	$111.40
Purchase #4	$41.89	4.451%	$43.7545	$43.75	$43.75	$43.80
Purchase #5	$65.88	9.589%	$72.1972	$72.20	$72.20	$72.20
Purchase #6	$104.77	3.819%	$108.7712	$108.77	$108.75	$108.80
Purchase #7	$144.94	11.641%	$161.8125	$161.81	$161.80	$161.80
7 purchase totals =	$707.54		$771.8484	$771.84	$771.80	$771.90