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	$100.71	5.738%	$106.4887	$106.49	$106.50	$106.50
Purchase #2	$194.82	6.719%	$207.91	$207.91	$207.90	$207.90
Purchase #3	$108.51	3.533%	$112.3437	$112.34	$112.35	$112.30
Purchase #4	$47.91	7.560%	$51.532	$51.53	$51.55	$51.50
Purchase #5	$16.67	10.661%	$18.4472	$18.45	$18.45	$18.40
Purchase #6	$117.42	5.220%	$123.5493	$123.55	$123.55	$123.50
Purchase #7	$238.85	9.236%	$260.9102	$260.91	$260.90	$260.90
7 purchase totals =	$824.89		$881.1811	$881.18	$881.20	$881.00