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	$140.33	13.734%	$159.6029	$159.60	$159.60	$159.60
Purchase #2	$112.90	8.823%	$122.8612	$122.86	$122.85	$122.90
Purchase #3	$164.63	7.273%	$176.6035	$176.60	$176.60	$176.60
Purchase #4	$153.81	6.846%	$164.3398	$164.34	$164.35	$164.30
Purchase #5	$31.48	4.222%	$32.8091	$32.81	$32.80	$32.80
Purchase #6	$249.45	12.261%	$280.0351	$280.04	$280.05	$280.00
Purchase #7	$126.43	3.636%	$131.027	$131.03	$131.05	$131.00
7 purchase totals =	$979.03		$1,067.2786	$1,067.28	$1,067.30	$1,067.20