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	$11.59	7.431%	$12.4513	$12.45	$12.45	$12.50
Purchase #2	$87.57	3.566%	$90.6927	$90.69	$90.70	$90.70
Purchase #3	$142.98	13.328%	$162.0364	$162.04	$162.05	$162.00
Purchase #4	$158.52	9.664%	$173.8394	$173.84	$173.85	$173.80
Purchase #5	$70.58	13.149%	$79.8606	$79.86	$79.85	$79.90
Purchase #6	$210.83	9.520%	$230.901	$230.90	$230.90	$230.90
Purchase #7	$152.95	10.405%	$168.8644	$168.86	$168.85	$168.90
7 purchase totals =	$835.02		$918.6458	$918.64	$918.65	$918.70