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	$245.66	5.634%	$259.5005	$259.50	$259.50	$259.50
Purchase #2	$164.69	3.495%	$170.4459	$170.45	$170.45	$170.40
Purchase #3	$36.58	11.532%	$40.7984	$40.80	$40.80	$40.80
Purchase #4	$78.60	5.704%	$83.0833	$83.08	$83.10	$83.10
Purchase #5	$241.90	12.795%	$272.8511	$272.85	$272.85	$272.90
Purchase #6	$118.69	11.548%	$132.3963	$132.40	$132.40	$132.40
Purchase #7	$23.78	4.541%	$24.8598	$24.86	$24.85	$24.90
7 purchase totals =	$909.90		$983.9353	$983.94	$983.95	$984.00