Did simony allowed people to avoide paying taxes to the church?

Historically... probably. "Simony" refers to, broadly, the purchase of Ecclesiastical office or privilege. At times when the church was in one of its more corrupt phases, there were probably families that "bought" a Cardinalship for a younger son with the expectation that that son would then proceed to give the family a pass when it came time to collect tithes ("Taxes" may not be the right Word to use here.)