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	$87.81	5.294%	$92.4587	$92.46	$92.45	$92.50
Purchase #2	$228.99	12.611%	$257.8679	$257.87	$257.85	$257.90
Purchase #3	$127.47	7.365%	$136.8582	$136.86	$136.85	$136.90
Purchase #4	$163.77	13.291%	$185.5367	$185.54	$185.55	$185.50
Purchase #5	$123.57	4.162%	$128.713	$128.71	$128.70	$128.70
Purchase #6	$194.47	9.286%	$212.5285	$212.53	$212.55	$212.50
Purchase #7	$131.60	4.127%	$137.0311	$137.03	$137.05	$137.00
7 purchase totals =	$1,057.68		$1,150.9941	$1,151.00	$1,151.00	$1,151.00