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	$138.49	13.792%	$157.5905	$157.59	$157.60	$157.60
Purchase #2	$22.76	9.175%	$24.8482	$24.85	$24.85	$24.80
Purchase #3	$58.93	10.453%	$65.09	$65.09	$65.10	$65.10
Purchase #4	$43.82	10.306%	$48.3361	$48.34	$48.35	$48.30
Purchase #5	$85.94	4.277%	$89.6157	$89.62	$89.60	$89.60
Purchase #6	$88.51	12.832%	$99.8676	$99.87	$99.85	$99.90
Purchase #7	$245.57	10.851%	$272.2168	$272.22	$272.20	$272.20
7 purchase totals =	$684.02		$757.5649	$757.58	$757.55	$757.50