Bring to a boil the sugar and milk, and let it boil exactly 6 1/2 minutes, stirring constantly. This is easiest on a gas stove, and the time may need to be adjusted depending on humidity. In another pan or bowl, combine the chocolate, oil, vanilla extract, and salt. Pour the hot mixture of sugar and milk over the other ingredients and blend together until all the chocolate has melted. Using a high powered hand mixer or stand mixer will make a smooth fudge. If you try to mix it by hand, it will start to harden before its mixed, and come out dry and grainy. Add raisins and gently mix into fudge during the last 30 seconds of mixing. Pour into a pan, and let set for six hours in the fridge until the fudge has set.