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	$12.35	9.738%	$13.5526	$13.55	$13.55	$13.60
Purchase #2	$108.84	6.664%	$116.0931	$116.09	$116.10	$116.10
Purchase #3	$94.35	6.247%	$100.244	$100.24	$100.25	$100.20
Purchase #4	$10.66	11.572%	$11.8936	$11.89	$11.90	$11.90
Purchase #5	$187.48	12.722%	$211.3312	$211.33	$211.35	$211.30
Purchase #6	$139.90	11.384%	$155.8262	$155.83	$155.85	$155.80
Purchase #7	$45.55	8.574%	$49.4555	$49.46	$49.45	$49.50
7 purchase totals =	$599.13		$658.3962	$658.39	$658.45	$658.40