The fee is 2 SEK ($0.2) per transaction - of course it's for tax evasion reasons, +25% extra margin makes a huge difference for a hair salon...
I never has a fee for any bank for depositing cash, even up to a few thousand. I really doubt that will happen unless you walk in with millions. In that case you will have more to worry about that fees.
And yes, it's a TINY amount. Stripe/Paypal charge several %