Can I create an option for donors to 501c3 to cover the transaction fee.

[FoHCCPS]

Is there a way to add to check out an option for donors to cover the transaction fee. We don't want to automatically charge them to cover the fee but offer the option?

We've found that if given the choice to donate an additional few dollars to cover a service cost, donors will.  

New to Square --The non-profit I volunteer for is fully volaunteer operated so we have no "professional" to ask. 

[GlassJudy]

Before you do anything to implement anything like what you want to do, you should check with your state's taxing authority to make sure passing transactions fees to customers is legal - it's not in every state, and I have no idea how you being a non-profit would affect that.

Right now, there is no way to do this directly, but several people have developed work arounds for it.  Most involve creating a 'Transaction Fee' item, then adding it to the sale.  Some people have calculated a rate to apply to the sale to account for the fact that whatever fees are added this way will also figure into the transaction fees that Square collects, and your fees will be determined by which version of Square you are using.

[FoHCCPS]

I don't want to pass anything off on to our donors.

I would like to ask them, via an option, yes or no--increase their donation to include the transaction fee. Which some platforms have. 

donate $21.30 to get the non-profit the full $20 donation.

The small commmunity school donors have asked how to do so.  

[puka]

Hey @FoHCCPS - Unfortunately, the feature you're describing is not available at this time. You would need to use one of the workarounds that @GlassJudy mentioned. A possible solution can be found at Can I Apply a Surcharge to Square Sales?