you beat me to that point.

i will also point out using a cash back card then pay the balance off every month in full you get FREE money.

before you start off on nothing is free rant. YES it's free $$$ that you are passing by with only cash attitude. merchants pay a percentage of the total charges they bill the Credit card company. the free $$$ comes from this fee. the problem is most consumers are usually not the brightest bulb in the box. they carry a balance every month and pay interest on it. in a LOT of cases the interest rate in in the 30% area. the free $$$ also comes from this.
now if you charge it with your cash back card then pay the bill in full it's exactly the same as paying cash in most situations and you get cash back at the end of the month. YES you can try to negotiate a lower bill by paying cash.it does work but not to often in my experiences. in most cases the person running the cash register will look at you like you are speaking a foreign language, worse yet they probably can't give you any discount if they actually understand what you are saying.