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	$105.98	9.758%	$116.3215	$116.32	$116.30	$116.30
Purchase #2	$207.78	3.603%	$215.2663	$215.27	$215.25	$215.30
Purchase #3	$201.41	10.447%	$222.4513	$222.45	$222.45	$222.50
Purchase #4	$138.53	12.308%	$155.5803	$155.58	$155.60	$155.60
Purchase #5	$121.68	8.349%	$131.8391	$131.84	$131.85	$131.80
Purchase #6	$202.25	7.643%	$217.708	$217.71	$217.70	$217.70
Purchase #7	$36.77	4.283%	$38.3449	$38.34	$38.35	$38.30
7 purchase totals =	$1,014.40		$1,097.5114	$1,097.51	$1,097.50	$1,097.50