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	$39.30	8.562%	$42.6649	$42.66	$42.65	$42.70
Purchase #2	$95.29	9.472%	$104.3159	$104.32	$104.30	$104.30
Purchase #3	$118.60	7.123%	$127.0479	$127.05	$127.05	$127.00
Purchase #4	$176.91	7.168%	$189.5909	$189.59	$189.60	$189.60
Purchase #5	$50.37	5.466%	$53.1232	$53.12	$53.10	$53.10
Purchase #6	$249.35	3.500%	$258.0773	$258.08	$258.10	$258.10
Purchase #7	$113.99	3.561%	$118.0492	$118.05	$118.05	$118.00
7 purchase totals =	$843.81		$892.8693	$892.87	$892.85	$892.80