Tone Change Rules in Taiwanese Chinese
 
1. If the original tone number is 5, pronounce it as tone number 7.
 
2. If the original tone number is 7, pronounce it as tone number 3.
 
3. If the original tone number is 3, pronounce it as tone number 2.
 
4. If the original tone number is 2, pronounce it as tone number 1.
 
5. If the original tone number is 1, pronounce it as tone number 7.
 
6. If the original tone number is 8 and the final consonant is not h (that is, it is p, t, or k), pronounce it as tone number 4.
 
7. If the original tone number is 4 and the final consonant is not h (that is, it is p, t, or k), pronounce it as tone number 8.
 
8. If the original tone number is 8 and the final consonant is h, pronounce it as tone number 3.
 
9. If the original tone number is 4 and the final consonant is h, pronounce it as tone number 2.
 

(From Wikipedia: "Taiwanese (linguistics)")