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	$10.63	13.770%	$12.0938	$12.09	$12.10	$12.10
Purchase #2	$71.30	11.553%	$79.5373	$79.54	$79.55	$79.50
Purchase #3	$112.53	13.580%	$127.8116	$127.81	$127.80	$127.80
Purchase #4	$52.45	13.724%	$59.6482	$59.65	$59.65	$59.60
Purchase #5	$137.47	3.568%	$142.3749	$142.37	$142.35	$142.40
Purchase #6	$121.25	4.833%	$127.11	$127.11	$127.10	$127.10
Purchase #7	$116.79	4.175%	$121.666	$121.67	$121.65	$121.70
7 purchase totals =	$622.42		$670.2418	$670.24	$670.20	$670.20