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	$122.89	13.479%	$139.4543	$139.45	$139.45	$139.50
Purchase #2	$205.94	8.105%	$222.6314	$222.63	$222.65	$222.60
Purchase #3	$212.42	12.781%	$239.5694	$239.57	$239.55	$239.60
Purchase #4	$11.92	13.337%	$13.5098	$13.51	$13.50	$13.50
Purchase #5	$9.77	4.437%	$10.2035	$10.20	$10.20	$10.20
Purchase #6	$157.27	4.812%	$164.8378	$164.84	$164.85	$164.80
Purchase #7	$246.93	13.750%	$280.8829	$280.88	$280.90	$280.90
7 purchase totals =	$967.14		$1,071.0891	$1,071.08	$1,071.10	$1,071.10