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	$188.60	10.723%	$208.8236	$208.82	$208.80	$208.80
Purchase #2	$100.51	3.249%	$103.7756	$103.78	$103.80	$103.80
Purchase #3	$20.58	5.756%	$21.7646	$21.76	$21.75	$21.80
Purchase #4	$203.96	9.110%	$222.5408	$222.54	$222.55	$222.50
Purchase #5	$164.97	10.430%	$182.1764	$182.18	$182.20	$182.20
Purchase #6	$18.51	4.492%	$19.3415	$19.34	$19.35	$19.30
Purchase #7	$149.77	3.826%	$155.5002	$155.50	$155.50	$155.50
7 purchase totals =	$846.90		$913.9227	$913.92	$913.95	$913.90