I crossed the US/Mexican border maybe 1000 times when i lived in San Diego, Had more than 10K maybe 800 of those times.
Anything to declare sir
ME: just some tacos
Im on my way.
They will never check your person, Even if they send you for a secondary inspection, they still wont check you personally unless you are acting like a real Douchebag.
PLEASE declare it . only if it more then 10000 , they will only hold you for a few min ,count it, you will sign it , and off you go..
if you won't , now it is a much longer delay