The giving of 1/10th of what we’ve been given, a tithe. Jacob chooses to offer this gift; he’s not told (commanded) to do this.
In the Old Testament the giving of 1/10th is considered a law to be practiced religiously. But what about the New Testament? Here we are given the guidance we are to live under as believers in Christ. [Here is also where some of my brethren may not agree with me].
Just as God wants us to choose to love and follow him, he wants us to choose to give back to the one that gives us all things. This passage does not define what the gift is to be, or even, where to give it to. It tells us that according to our heart and to be a cheerful giver.
So, how much are you to give, to tithe? You give what your heart cheerfully gives. God would rather have a penny given in the right spirit (attitude) than a million dollars in the wrong.
Your tithe is a gift from you back to the one who gives all things as a thank you; a recognition of where what you have came from. How much is it? Whatever your heart tells you. Pray about it. Study on it. Discuss it. Perhaps you have time but no money; then give time. Perhaps you have money but (you think) no time, then pray about where to give it.