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	$26.51	12.637%	$29.8601	$29.86	$29.85	$29.90
Purchase #2	$104.69	3.663%	$108.5248	$108.52	$108.50	$108.50
Purchase #3	$123.87	12.531%	$139.3921	$139.39	$139.40	$139.40
Purchase #4	$45.91	8.358%	$49.7472	$49.75	$49.75	$49.70
Purchase #5	$234.38	9.766%	$257.2696	$257.27	$257.25	$257.30
Purchase #6	$108.47	7.384%	$116.4794	$116.48	$116.50	$116.50
Purchase #7	$40.93	5.665%	$43.2487	$43.25	$43.25	$43.20
7 purchase totals =	$684.76		$744.5219	$744.52	$744.50	$744.50