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	$28.27	6.698%	$30.1635	$30.16	$30.15	$30.20
Purchase #2	$50.55	4.561%	$52.8556	$52.86	$52.85	$52.90
Purchase #3	$249.42	4.792%	$261.3722	$261.37	$261.35	$261.40
Purchase #4	$74.37	12.397%	$83.5896	$83.59	$83.60	$83.60
Purchase #5	$249.29	6.121%	$264.549	$264.55	$264.55	$264.50
Purchase #6	$74.94	12.710%	$84.4649	$84.46	$84.45	$84.50
Purchase #7	$155.93	12.161%	$174.8926	$174.89	$174.90	$174.90
7 purchase totals =	$882.77		$951.8874	$951.88	$951.85	$952.00