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	$242.79	5.243%	$255.5195	$255.52	$255.50	$255.50
Purchase #2	$113.72	8.494%	$123.3794	$123.38	$123.40	$123.40
Purchase #3	$115.57	3.750%	$119.9039	$119.90	$119.90	$119.90
Purchase #4	$14.91	11.826%	$16.6733	$16.67	$16.65	$16.70
Purchase #5	$217.85	5.565%	$229.9734	$229.97	$229.95	$230.00
Purchase #6	$128.55	7.278%	$137.9059	$137.91	$137.90	$137.90
Purchase #7	$109.97	12.379%	$123.5832	$123.58	$123.60	$123.60
7 purchase totals =	$943.36		$1,006.9386	$1,006.93	$1,006.90	$1,007.00