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	$12.64	7.551%	$13.5944	$13.59	$13.60	$13.60
Purchase #2	$238.30	9.266%	$260.3809	$260.38	$260.40	$260.40
Purchase #3	$94.76	6.383%	$100.8085	$100.81	$100.80	$100.80
Purchase #4	$207.95	12.447%	$233.8335	$233.83	$233.85	$233.80
Purchase #5	$75.64	3.635%	$78.3895	$78.39	$78.40	$78.40
Purchase #6	$50.92	10.822%	$56.4306	$56.43	$56.45	$56.40
Purchase #7	$208.86	5.798%	$220.9697	$220.97	$220.95	$221.00
7 purchase totals =	$889.07		$964.4071	$964.40	$964.45	$964.40