Soft costs in EFTPOS and credit cards are extra costs that you have but are taken into account formally. But I do suggest that you run through them as they do add up.
Examples would be
Incorrect keying in of information
A sale of $23.44 is incorrectly processed at $13.44, well that is a $10 cost. If your business made 10 of these a month, your soft cost here is $100/month
Time is taken to key in the transactions
If a transaction takes a staff member 10 seconds to do and you did 2,000 transactions a month, well your soft cost here is 5.5 hours, say staff time is $33/hour, this item is about $150/month
If it takes you an hour a week to reconcile your point of sale software to the bank records well there are here another 4 hours.
There are many others that you can add, I am sure to the list.
Typically on a non-integrated, I would expect that these costs to a merchant are about $400/month, on an integrated EFTPOS system about $200/month.