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	$132.95	3.397%	$137.4663	$137.47	$137.45	$137.50
Purchase #2	$35.45	12.832%	$39.9989	$40.00	$40.00	$40.00
Purchase #3	$248.28	13.773%	$282.4756	$282.48	$282.50	$282.50
Purchase #4	$214.90	7.261%	$230.5039	$230.50	$230.50	$230.50
Purchase #5	$74.39	5.566%	$78.5305	$78.53	$78.55	$78.50
Purchase #6	$105.61	12.548%	$118.8619	$118.86	$118.85	$118.90
Purchase #7	$10.53	8.384%	$11.4128	$11.41	$11.40	$11.40
7 purchase totals =	$822.11		$899.2499	$899.25	$899.25	$899.30