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	$135.48	6.758%	$144.6357	$144.64	$144.65	$144.60
Purchase #2	$214.72	7.393%	$230.5942	$230.59	$230.60	$230.60
Purchase #3	$143.89	10.275%	$158.6747	$158.67	$158.65	$158.70
Purchase #4	$31.98	11.698%	$35.721	$35.72	$35.70	$35.70
Purchase #5	$137.49	11.378%	$153.1336	$153.13	$153.15	$153.10
Purchase #6	$6.88	9.770%	$7.5522	$7.55	$7.55	$7.60
Purchase #7	$59.42	11.160%	$66.0513	$66.05	$66.05	$66.10
7 purchase totals =	$729.86		$796.3627	$796.35	$796.35	$796.40