I had a new script for Oxymorphone 5mg to be

I had a new script for Oxymorphone 5mg to be taken 1 5 times daily. My drug store did not have that MG and was to order it. When it was picked up and brought to me, it is 10 mg tabs to be taken 1/2 5 times a day. The tabs are not scored and are made by two different companies. I looked them up on the net. The one pill is Opana, time released, generic version. Second is Oxymorphone, time released. Is it not unsafe to cut these tablets in half?