Everything you flush will affect your tank in some way and may lead to you needing to conduct a septic system repair in the long run. When toilet paper is flushed, it settles to the bottom of the tank like other solids do. Bacteria does decompose some of this waste, but much more of it simply ends up becoming sludge.
Beside this, how do you know if toilet paper is septic safe?
You can now see how much the toilet paper has broken down. If the toilet paper is still quite intact then you may want to consider a different brand. If the toilet paper is broken up into very small pieces, then you are using a septic safe toilet paper already.