I make all charity payments on one day when there are no other payments going through my bank account. I then send the payment confirmation with my tax declaration, lumping all donations together.
I show this amount under both local and federal. The tax office has accepted this without question for a couple of decades...
The limit on the federal level is 20% of the taxable income after this deduction (which makes it 1/6 before). The maximum on the cantonal level differs by canton, in NE this appears to be 5%, 50% in TI, no limit in BL.
Regulations for political parties are separately regulated.