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	$6.77	5.378%	$7.1341	$7.13	$7.15	$7.10
Purchase #2	$105.56	10.828%	$116.99	$116.99	$117.00	$117.00
Purchase #3	$79.66	13.462%	$90.3838	$90.38	$90.40	$90.40
Purchase #4	$68.70	6.103%	$72.8928	$72.89	$72.90	$72.90
Purchase #5	$14.72	7.725%	$15.8571	$15.86	$15.85	$15.90
Purchase #6	$179.40	8.490%	$194.6311	$194.63	$194.65	$194.60
Purchase #7	$18.56	4.707%	$19.4336	$19.43	$19.45	$19.40
7 purchase totals =	$473.37		$517.3225	$517.31	$517.40	$517.30