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	$7.76	9.237%	$8.4768	$8.48	$8.50	$8.50
Purchase #2	$118.27	8.256%	$128.0344	$128.03	$128.05	$128.00
Purchase #3	$95.53	5.182%	$100.4804	$100.48	$100.50	$100.50
Purchase #4	$225.79	9.284%	$246.7523	$246.75	$246.75	$246.80
Purchase #5	$241.78	3.533%	$250.3221	$250.32	$250.30	$250.30
Purchase #6	$100.51	4.293%	$104.8249	$104.82	$104.80	$104.80
Purchase #7	$123.39	12.289%	$138.5534	$138.55	$138.55	$138.60
7 purchase totals =	$913.03		$977.4443	$977.43	$977.45	$977.50