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	$63.86	13.179%	$72.2761	$72.28	$72.30	$72.30
Purchase #2	$13.51	11.427%	$15.0538	$15.05	$15.05	$15.10
Purchase #3	$237.75	8.634%	$258.2773	$258.28	$258.30	$258.30
Purchase #4	$60.92	10.175%	$67.1186	$67.12	$67.10	$67.10
Purchase #5	$181.84	7.396%	$195.2889	$195.29	$195.30	$195.30
Purchase #6	$134.83	3.694%	$139.8106	$139.81	$139.80	$139.80
Purchase #7	$206.38	11.694%	$230.5141	$230.51	$230.50	$230.50
7 purchase totals =	$899.09		$978.3394	$978.34	$978.35	$978.40