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	$127.82	9.196%	$139.5743	$139.57	$139.55	$139.60
Purchase #2	$199.91	12.672%	$225.2426	$225.24	$225.25	$225.20
Purchase #3	$159.60	5.513%	$168.3987	$168.40	$168.40	$168.40
Purchase #4	$10.60	4.564%	$11.0838	$11.08	$11.10	$11.10
Purchase #5	$201.62	3.339%	$208.3521	$208.35	$208.35	$208.40
Purchase #6	$50.76	6.522%	$54.0706	$54.07	$54.05	$54.10
Purchase #7	$97.54	6.286%	$103.6714	$103.67	$103.65	$103.70
7 purchase totals =	$847.85		$910.3935	$910.38	$910.35	$910.50