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	$83.89	7.105%	$89.8504	$89.85	$89.85	$89.90
Purchase #2	$173.45	6.859%	$185.3469	$185.35	$185.35	$185.30
Purchase #3	$19.58	11.491%	$21.8299	$21.83	$21.85	$21.80
Purchase #4	$117.92	4.536%	$123.2689	$123.27	$123.25	$123.30
Purchase #5	$202.53	6.105%	$214.8945	$214.89	$214.90	$214.90
Purchase #6	$12.56	3.426%	$12.9903	$12.99	$13.00	$13.00
Purchase #7	$212.76	12.526%	$239.4103	$239.41	$239.40	$239.40
7 purchase totals =	$822.69		$887.5912	$887.59	$887.60	$887.60