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	$142.62	11.205%	$158.6006	$158.60	$158.60	$158.60
Purchase #2	$166.34	12.587%	$187.2772	$187.28	$187.30	$187.30
Purchase #3	$37.32	8.631%	$40.5411	$40.54	$40.55	$40.50
Purchase #4	$90.29	4.735%	$94.5652	$94.57	$94.55	$94.60
Purchase #5	$228.42	6.106%	$242.3673	$242.37	$242.35	$242.40
Purchase #6	$19.52	8.845%	$21.2465	$21.25	$21.25	$21.20
Purchase #7	$204.64	4.209%	$213.2533	$213.25	$213.25	$213.30
7 purchase totals =	$889.15		$957.8512	$957.86	$957.85	$957.90