Sims in the Peninsula State pay the following taxes, every year ending in 5 or 0 (every 5 years):
10% on the total of: Home Value + Bank Balance (except college fund & retirement*) + Cash
House Credit: $1000 (and Sims whose home has a negative balance (mortgage), have the amount they still owe deducted from their total tax owed. Together with deductions, this can cause them to get a refund instead of owe on taxes, see Refunds, below.)
Child Credit: $1500 (per child)
College Credit: $1500
Business Credit: 500 for Rank 1 up to 5500 Rank 10
Farm Credit: $2000
Married/Joined Credit: $1500 per couple
Retired sims are tax exempt, but families who live with them are not.
*Up to $30,000 in savings can be considered to be for retirement, which is not taxable.
If deductions are greater than the total owed, the difference is refunded to the family.
Thanks to many other Sims 2 bloggers, most specifically Sullivan, whose numbers I have copied.