I don't see that anywhere in your capx, but if you set the variable to 25*1.05, then that variable is just set at 26.25.
if you want to add 5% each time a button is clicked, then you would
on clicked | set variable "whatever" = whatever * 1.05.
this will add 5 per cent to the current number in the variable "whatever".
I would suggest naming your different buttons to something relevant
and not naming your variable a number (doesn't make much sense, if the number is going to change)