SEP contribution - how does the IRS know?

I have always wondered about something. TT asks if you have contributed to a SEP IRA. I do this every year. I figure (but do not file) my taxes, then send a payment to my IRA (because I do not know the amount I am allowed to contribute until I do my taxes), and then when that check clears and the payment is received (by the IRA bank) then I file my taxes. I am wondering if the IRS checks to make sure that the IRA payment has cleared? Does this make sense? In other words, does the IRS check to make sure that the IRA payments people claim to make, are actually made? (I would imagine so). Thank you.