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	$150.29	3.437%	$155.4555	$155.46	$155.45	$155.50
Purchase #2	$95.42	3.789%	$99.0355	$99.04	$99.05	$99.00
Purchase #3	$151.58	10.403%	$167.3489	$167.35	$167.35	$167.30
Purchase #4	$49.89	5.337%	$52.5526	$52.55	$52.55	$52.60
Purchase #5	$124.93	11.461%	$139.2482	$139.25	$139.25	$139.20
Purchase #6	$195.37	9.708%	$214.3365	$214.34	$214.35	$214.30
Purchase #7	$142.81	8.435%	$154.856	$154.86	$154.85	$154.90
7 purchase totals =	$910.29		$982.8332	$982.85	$982.85	$982.80