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	$52.73	7.283%	$56.5703	$56.57	$56.55	$56.60
Purchase #2	$35.64	13.528%	$40.4614	$40.46	$40.45	$40.50
Purchase #3	$62.28	7.264%	$66.804	$66.80	$66.80	$66.80
Purchase #4	$7.71	11.354%	$8.5854	$8.59	$8.60	$8.60
Purchase #5	$44.94	8.823%	$48.9051	$48.91	$48.90	$48.90
Purchase #6	$213.98	11.314%	$238.1897	$238.19	$238.20	$238.20
Purchase #7	$90.88	4.835%	$95.274	$95.27	$95.25	$95.30
7 purchase totals =	$508.16		$554.7899	$554.79	$554.75	$554.90