Can I offer incentives for people to donate to a charitable cause?

It depends on your states gambling laws. But as long as you dont make a big production of it no one will care.

Just giving is good anytime, it IS probably the only thing that separates the saints from the sinners! But, if you are Christian, why not find a wonderful Christian charity that does awesome good to whomever is in need like: Samaritan's Purse or Operation Blessing who both send food, medicine, doctors, clothing the needy, etc. like down in Peru after this devastating earthquake; or like the immediate and continued help and support of providing food and shelter (temporary and permanent) for the victims of hurricane Katrina in the Gulf. You don't have to tithe to a "church/denomination", but can tithe to a Christian organization. Never forget the great world-wide giver of so much care and help: The Salvation Army. Tithing is giving 10% to God's care and work and it's out of your control! God isn't trying to GET your money, He's trying to BLESS your 90% that you control. Read Hebrews 7: 2 thru 8.., and I see this as explaining that Abraham paid tithes (before the LAW was given) to Melchisedec.. and this priest blessed Abraham and as in verse 6 that had the promises already.. and verse 7; the less (Abraham) is blessed of the better (Melchisedec.. the High Priest). This High Priest was appointed by God Himself (a forerunner and representation of Jesus Christ) and has no record of death; and the scripture witnesses that he lives. He received tithes; verse 8 says that the Jewish priesthood received tithes and they are NOT the permanent priesthood according to God, only a "copy" of the REAL, because they DIE in the natural and they blessed the people, but couldn't BE the ultimate BLESSER, because they are not truly "the better". The REAL "better" is Jesus, Himself! See? and when we tithe NOW..., (NOT AN OLD TESTAMENT LAW, but an "all-time" God-law), we tithe unto JESUS, our High Priest (Hebrews 3:1) and it is witnessed that HE LIVES! Tithing is NOT an Old Testament or MOSIACAL LAW rule. It IS God's law of money management for God's people. We dare NOT take what is God's! Ask Adam and Eve what happens when you touch that which is designated as belonging to God.