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	$56.87	13.360%	$64.4678	$64.47	$64.45	$64.50
Purchase #2	$11.68	7.277%	$12.53	$12.53	$12.55	$12.50
Purchase #3	$102.45	3.217%	$105.7458	$105.75	$105.75	$105.70
Purchase #4	$173.91	4.610%	$181.9273	$181.93	$181.95	$181.90
Purchase #5	$25.83	13.177%	$29.2336	$29.23	$29.25	$29.20
Purchase #6	$128.85	10.676%	$142.606	$142.61	$142.60	$142.60
Purchase #7	$38.83	11.722%	$43.3817	$43.38	$43.40	$43.40
7 purchase totals =	$538.42		$579.8922	$579.90	$579.95	$579.80