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	$35.32	13.472%	$40.0783	$40.08	$40.10	$40.10
Purchase #2	$30.91	4.809%	$32.3965	$32.40	$32.40	$32.40
Purchase #3	$78.83	6.149%	$83.6773	$83.68	$83.70	$83.70
Purchase #4	$207.64	8.789%	$225.8895	$225.89	$225.90	$225.90
Purchase #5	$29.41	5.843%	$31.1284	$31.13	$31.15	$31.10
Purchase #6	$22.57	10.313%	$24.8976	$24.90	$24.90	$24.90
Purchase #7	$219.86	6.189%	$233.4671	$233.47	$233.45	$233.50
7 purchase totals =	$624.54		$671.5347	$671.55	$671.60	$671.60