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	$28.44	9.480%	$31.1361	$31.14	$31.15	$31.10
Purchase #2	$142.40	5.720%	$150.5453	$150.55	$150.55	$150.50
Purchase #3	$247.43	8.734%	$269.0405	$269.04	$269.05	$269.00
Purchase #4	$95.59	4.622%	$100.0082	$100.01	$100.00	$100.00
Purchase #5	$19.75	3.431%	$20.4276	$20.43	$20.45	$20.40
Purchase #6	$158.62	11.161%	$176.3236	$176.32	$176.30	$176.30
Purchase #7	$84.30	13.733%	$95.8769	$95.88	$95.90	$95.90
7 purchase totals =	$776.53		$843.3582	$843.37	$843.40	$843.20