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	$34.80	13.843%	$39.6174	$39.62	$39.60	$39.60
Purchase #2	$59.38	10.532%	$65.6339	$65.63	$65.65	$65.60
Purchase #3	$121.55	10.661%	$134.5084	$134.51	$134.50	$134.50
Purchase #4	$9.27	11.364%	$10.3234	$10.32	$10.30	$10.30
Purchase #5	$103.80	10.282%	$114.4727	$114.47	$114.45	$114.50
Purchase #6	$94.78	8.283%	$102.6306	$102.63	$102.65	$102.60
Purchase #7	$111.32	10.735%	$123.2702	$123.27	$123.25	$123.30
7 purchase totals =	$534.90		$590.4566	$590.45	$590.40	$590.40