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	$117.38	5.587%	$123.938	$123.94	$123.95	$123.90
Purchase #2	$11.71	13.208%	$13.2567	$13.26	$13.25	$13.30
Purchase #3	$145.84	6.131%	$154.7815	$154.78	$154.80	$154.80
Purchase #4	$132.43	10.765%	$146.6861	$146.69	$146.70	$146.70
Purchase #5	$76.80	10.866%	$85.1451	$85.15	$85.15	$85.10
Purchase #6	$165.95	6.619%	$176.9342	$176.93	$176.95	$176.90
Purchase #7	$133.98	5.821%	$141.779	$141.78	$141.80	$141.80
7 purchase totals =	$784.09		$842.5206	$842.53	$842.60	$842.50