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	$225.83	10.377%	$249.2644	$249.26	$249.25	$249.30
Purchase #2	$32.40	5.707%	$34.2491	$34.25	$34.25	$34.20
Purchase #3	$128.85	7.801%	$138.9016	$138.90	$138.90	$138.90
Purchase #4	$146.32	5.459%	$154.3076	$154.31	$154.30	$154.30
Purchase #5	$134.40	12.699%	$151.4675	$151.47	$151.45	$151.50
Purchase #6	$123.90	13.156%	$140.2003	$140.20	$140.20	$140.20
Purchase #7	$90.68	5.716%	$95.8633	$95.86	$95.85	$95.90
7 purchase totals =	$882.38		$964.2538	$964.25	$964.20	$964.30