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	$8.84	13.480%	$10.0316	$10.03	$10.05	$10.00
Purchase #2	$132.54	13.856%	$150.9047	$150.90	$150.90	$150.90
Purchase #3	$138.51	3.161%	$142.8883	$142.89	$142.90	$142.90
Purchase #4	$116.71	13.706%	$132.7063	$132.71	$132.70	$132.70
Purchase #5	$213.60	4.171%	$222.5093	$222.51	$222.50	$222.50
Purchase #6	$146.50	4.128%	$152.5475	$152.55	$152.55	$152.50
Purchase #7	$135.77	12.493%	$152.7317	$152.73	$152.75	$152.70
7 purchase totals =	$892.47		$964.3194	$964.32	$964.35	$964.20