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	$32.73	4.669%	$34.2582	$34.26	$34.25	$34.30
Purchase #2	$45.64	5.253%	$48.0375	$48.04	$48.05	$48.00
Purchase #3	$39.44	3.675%	$40.8894	$40.89	$40.90	$40.90
Purchase #4	$248.98	12.524%	$280.1623	$280.16	$280.15	$280.20
Purchase #5	$216.98	7.795%	$233.8936	$233.89	$233.90	$233.90
Purchase #6	$10.49	9.306%	$11.4662	$11.47	$11.45	$11.50
Purchase #7	$162.63	5.659%	$171.8332	$171.83	$171.85	$171.80
7 purchase totals =	$756.89		$820.5404	$820.54	$820.55	$820.60