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	$14.97	3.527%	$15.498	$15.50	$15.50	$15.50
Purchase #2	$132.99	13.105%	$150.4183	$150.42	$150.40	$150.40
Purchase #3	$139.72	13.274%	$158.2664	$158.27	$158.25	$158.30
Purchase #4	$157.54	5.866%	$166.7813	$166.78	$166.80	$166.80
Purchase #5	$184.57	4.260%	$192.4327	$192.43	$192.45	$192.40
Purchase #6	$125.67	4.461%	$131.2761	$131.28	$131.30	$131.30
Purchase #7	$222.85	3.265%	$230.1261	$230.13	$230.15	$230.10
7 purchase totals =	$978.31		$1,044.7989	$1,044.81	$1,044.85	$1,044.80