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	$108.84	6.657%	$116.0855	$116.09	$116.10	$116.10
Purchase #2	$94.80	5.432%	$99.9495	$99.95	$99.95	$99.90
Purchase #3	$93.84	12.297%	$105.3795	$105.38	$105.40	$105.40
Purchase #4	$66.72	8.763%	$72.5667	$72.57	$72.55	$72.60
Purchase #5	$126.79	12.324%	$142.4156	$142.42	$142.40	$142.40
Purchase #6	$212.82	10.397%	$234.9469	$234.95	$234.95	$234.90
Purchase #7	$139.36	4.237%	$145.2647	$145.26	$145.25	$145.30
7 purchase totals =	$843.17		$916.6084	$916.62	$916.60	$916.60