Sales sheet- advanced if/sumif question

I have two worksheets that I am creating, one is a Sales sheet and the other is a Contact list. The Sales sheet will have a seperate row for each item a customer buys. In the Contact sheet, for each customer, I would like to have a total of his purchases. What formula can I use to make the Contact list automatically total for each individual from the Sales sheet?

Attached is an image of the two sheets.