I think you misunderstand how standard vs. itemized deductions work. Your first three charitable contributions didn't change your refund because your TOTAL itemized deductions at that time were LESS than your standard deduction (which everyone who does NOT itemize gets), thus TurboTax gave you the standard deduction as it was more advantageous to you. (You can override it but it's not a good idea unless you MUST itemize, usually if you file separately and your spouse itemizes -- itself not a good idea for most couples.)
Once you entered the fourth contribution your total itemized deductions exceeded the standard deduction, so it AND the fifth contribution reduced your taxes as now itemizing is the better option for you.
All your contributions are "deductible" per se; it's just that itemized deductions in general don't help you until the total exceeds your standard deduction. (It will be even worse next year as Trump's tax bill increases the standard deduction substantially.)
