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	$6.39	7.733%	$6.8841	$6.88	$6.90	$6.90
Purchase #2	$128.72	9.566%	$141.0334	$141.03	$141.05	$141.00
Purchase #3	$52.34	6.750%	$55.873	$55.87	$55.85	$55.90
Purchase #4	$109.85	11.844%	$122.8606	$122.86	$122.85	$122.90
Purchase #5	$99.42	6.217%	$105.6009	$105.60	$105.60	$105.60
Purchase #6	$134.72	7.231%	$144.4616	$144.46	$144.45	$144.50
Purchase #7	$200.49	12.497%	$225.5452	$225.55	$225.55	$225.50
7 purchase totals =	$731.93		$802.2588	$802.25	$802.25	$802.30