When To Quit Searching A Box Of Coins

I had a batch of cwr's(about $20 worth) and was findig nothing. When I got to the last coin in the last roll I found a 1999 WAM. You never know when the freasure is going tosurface!

Last night I finished the exasperatingly bad box of pennies that I was thinking about quitting. Here's the stats:

copper (all years) 344
Copper (1982) 44
Canadian (all years) 6
LWC - none
2009 (all types) 4
AU - BU: 8

Prior to this my last batch four boxes had (not counting the above box):
Copper (all years) 2009
Copper (1982) 37 (correction)
Canadian (all years) 37
LWC - 103
Can't speak to the 2009's nor AU/BU coins as I don't keep an accurate count on those items

The box I just finished had 15% copper but I've had worse. In fact my worse batch of 4 boxes had 15% copper but it didn't have any figures for 1982 coins.

So I'm going to lay off the pennies for awhile now and look into doing some halves and see how much pain those are going to give me. Hopefully I can fill the remaining holes in my Kennedy set before I get to work on the proof Jefferson set.

I have 5 boxes of nickels to look through and then separate them down by years and mint mark. I'm not expecting much but am willing to work at it.