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	$237.59	8.108%	$256.8538	$256.85	$256.85	$256.90
Purchase #2	$148.78	10.195%	$163.9481	$163.95	$163.95	$163.90
Purchase #3	$108.35	13.717%	$123.2124	$123.21	$123.20	$123.20
Purchase #4	$211.54	10.377%	$233.4915	$233.49	$233.50	$233.50
Purchase #5	$44.31	13.225%	$50.17	$50.17	$50.15	$50.20
Purchase #6	$218.87	10.311%	$241.4377	$241.44	$241.45	$241.40
Purchase #7	$35.80	12.737%	$40.3598	$40.36	$40.35	$40.40
7 purchase totals =	$1,005.24		$1,109.4733	$1,109.47	$1,109.45	$1,109.50