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	$37.27	8.692%	$40.5095	$40.51	$40.50	$40.50
Purchase #2	$23.59	3.558%	$24.4293	$24.43	$24.45	$24.40
Purchase #3	$127.49	4.189%	$132.8306	$132.83	$132.85	$132.80
Purchase #4	$249.29	12.831%	$281.2764	$281.28	$281.30	$281.30
Purchase #5	$116.51	3.589%	$120.6915	$120.69	$120.70	$120.70
Purchase #6	$126.81	10.136%	$139.6635	$139.66	$139.65	$139.70
Purchase #7	$92.25	9.272%	$100.8034	$100.80	$100.80	$100.80
7 purchase totals =	$773.21		$840.2042	$840.20	$840.25	$840.20