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	$6.53	4.522%	$6.8253	$6.83	$6.85	$6.80
Purchase #2	$132.59	10.337%	$146.2958	$146.30	$146.30	$146.30
Purchase #3	$213.53	9.741%	$234.33	$234.33	$234.35	$234.30
Purchase #4	$127.60	3.313%	$131.8274	$131.83	$131.85	$131.80
Purchase #5	$171.49	4.874%	$179.8484	$179.85	$179.85	$179.80
Purchase #6	$133.45	7.304%	$143.1972	$143.20	$143.20	$143.20
Purchase #7	$120.87	12.804%	$136.3462	$136.35	$136.35	$136.30
7 purchase totals =	$906.06		$978.6703	$978.69	$978.75	$978.50