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	$239.72	7.116%	$256.7785	$256.78	$256.80	$256.80
Purchase #2	$188.95	6.164%	$200.5969	$200.60	$200.60	$200.60
Purchase #3	$16.93	13.315%	$19.1842	$19.18	$19.20	$19.20
Purchase #4	$102.39	6.389%	$108.9317	$108.93	$108.95	$108.90
Purchase #5	$38.57	12.709%	$43.4719	$43.47	$43.45	$43.50
Purchase #6	$72.69	8.307%	$78.7284	$78.73	$78.75	$78.70
Purchase #7	$149.52	9.568%	$163.8261	$163.83	$163.85	$163.80
7 purchase totals =	$808.77		$871.5177	$871.52	$871.60	$871.50