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	$245.71	4.136%	$255.8726	$255.87	$255.85	$255.90
Purchase #2	$25.97	5.270%	$27.3386	$27.34	$27.35	$27.30
Purchase #3	$47.69	9.701%	$52.3164	$52.32	$52.30	$52.30
Purchase #4	$27.77	7.662%	$29.8977	$29.90	$29.90	$29.90
Purchase #5	$72.52	8.519%	$78.698	$78.70	$78.70	$78.70
Purchase #6	$55.53	8.836%	$60.4366	$60.44	$60.45	$60.40
Purchase #7	$154.37	4.733%	$161.6763	$161.68	$161.70	$161.70
7 purchase totals =	$629.56		$666.2362	$666.25	$666.25	$666.20