What is the proper tithe for a theft?

I'm a thief and I am also religious. I feel that I should be giving a portion of my ill gotten goods to the church. At my church we are to give 10% of our income each month, and I am not sure if the tithe should be 10% of the goods value at retail or the amount of money I make from the selling of the goods. As I usually sell for a third of retail price. For instance if I steal a pair of shoes that are $100. If I sell the shoes for $30 then I would have to make 3 pairs of shoes to get my 10%.