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	$236.90	13.245%	$268.2774	$268.28	$268.30	$268.30
Purchase #2	$163.45	13.340%	$185.2542	$185.25	$185.25	$185.30
Purchase #3	$225.78	12.249%	$253.4358	$253.44	$253.45	$253.40
Purchase #4	$72.32	12.733%	$81.5285	$81.53	$81.55	$81.50
Purchase #5	$100.37	11.449%	$111.8614	$111.86	$111.85	$111.90
Purchase #6	$241.29	4.504%	$252.1577	$252.16	$252.15	$252.20
Purchase #7	$224.79	5.560%	$237.2883	$237.29	$237.30	$237.30
7 purchase totals =	$1,264.90		$1,389.8033	$1,389.81	$1,389.85	$1,389.90