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	$150.57	5.499%	$158.8498	$158.85	$158.85	$158.80
Purchase #2	$171.42	11.153%	$190.5385	$190.54	$190.55	$190.50
Purchase #3	$142.34	3.159%	$146.8365	$146.84	$146.85	$146.80
Purchase #4	$165.44	13.271%	$187.3955	$187.40	$187.40	$187.40
Purchase #5	$100.95	8.550%	$109.5812	$109.58	$109.60	$109.60
Purchase #6	$117.35	12.330%	$131.8193	$131.82	$131.80	$131.80
Purchase #7	$29.74	4.720%	$31.1437	$31.14	$31.15	$31.10
7 purchase totals =	$877.81		$956.1645	$956.17	$956.20	$956.00