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	$81.55	12.305%	$91.5847	$91.58	$91.60	$91.60
Purchase #2	$164.96	6.724%	$176.0519	$176.05	$176.05	$176.10
Purchase #3	$15.84	13.159%	$17.9244	$17.92	$17.90	$17.90
Purchase #4	$142.71	11.374%	$158.9418	$158.94	$158.95	$158.90
Purchase #5	$214.43	3.649%	$222.2546	$222.25	$222.25	$222.30
Purchase #6	$91.98	8.578%	$99.87	$99.87	$99.85	$99.90
Purchase #7	$46.43	10.857%	$51.4709	$51.47	$51.45	$51.50
7 purchase totals =	$757.90		$818.0983	$818.08	$818.05	$818.20