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	$15.29	8.552%	$16.5976	$16.60	$16.60	$16.60
Purchase #2	$34.32	11.503%	$38.2678	$38.27	$38.25	$38.30
Purchase #3	$95.41	9.431%	$104.4081	$104.41	$104.40	$104.40
Purchase #4	$67.66	6.734%	$72.2162	$72.22	$72.20	$72.20
Purchase #5	$135.60	11.407%	$151.0679	$151.07	$151.05	$151.10
Purchase #6	$158.89	6.533%	$169.2703	$169.27	$169.25	$169.30
Purchase #7	$142.58	5.632%	$150.6101	$150.61	$150.60	$150.60
7 purchase totals =	$649.75		$702.4380	$702.45	$702.35	$702.50