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	$33.87	13.672%	$38.5007	$38.50	$38.50	$38.50
Purchase #2	$20.79	5.155%	$21.8617	$21.86	$21.85	$21.90
Purchase #3	$241.74	9.733%	$265.2686	$265.27	$265.25	$265.30
Purchase #4	$10.45	11.421%	$11.6435	$11.64	$11.65	$11.60
Purchase #5	$30.54	12.752%	$34.4345	$34.43	$34.45	$34.40
Purchase #6	$142.43	7.191%	$152.6721	$152.67	$152.65	$152.70
Purchase #7	$248.78	9.441%	$272.2673	$272.27	$272.25	$272.30
7 purchase totals =	$728.60		$796.6484	$796.64	$796.60	$796.70