Is it a sin to go a casino and play the slot machines for entertainment when your bills and tithes have been paid?
To willingly and knowingly break a commandment of God is by definition a sin. This is what lds.org has to say regarding gambling:
“The Church of Jesus Christ of Latter-day Saints is opposed to gambling, including lotteries sponsored by governments. Church leaders have encouraged Church members to join with others in opposing the legalization and government sponsorship of any form of gambling.”
When it comes to sin. many of us seek to find an exception or an excuse as to why a particular commandment does not apply to us in our situation. Sometimes this is correct but not often. Such exceptions can only come from God. Take your question and your desire to God and ask him.