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	$73.26	13.638%	$83.2512	$83.25	$83.25	$83.30
Purchase #2	$69.27	8.128%	$74.9003	$74.90	$74.90	$74.90
Purchase #3	$158.87	4.378%	$165.8253	$165.83	$165.85	$165.80
Purchase #4	$114.76	7.778%	$123.686	$123.69	$123.70	$123.70
Purchase #5	$92.66	13.687%	$105.3424	$105.34	$105.35	$105.30
Purchase #6	$239.71	8.384%	$259.8073	$259.81	$259.80	$259.80
Purchase #7	$8.87	13.665%	$10.0821	$10.08	$10.10	$10.10
7 purchase totals =	$757.40		$822.8946	$822.90	$822.95	$822.90