There are 3 sounds for regular plural nouns. They are governed by the ending sound (not necessarily the ending letter) of the singular form.
If the ending sound is voiced, the 's' is pronounced /z/. Those voiced sounds are /b/,/g/, /d/, /v/, /l/,/r/, /m/, /n/, /ŋ/ (as in 'song'), and /ð/ (as in 'smooth').
All vowel sounds are also voiced, so for example 'day' would receive the plural /z/ sound.
If the ending sound is voiceless, the 's' is pronounced /s/. Those voiceless sounds are /p/,/k/, /t/, /f/, and /θ/ (as in 'tooth')
There are five exceptions, which also cover any time the plural is formed with 'es'. Note that the 'es' plural also adds an extra syllable which is pronounced /ɪz/.
Those five exceptions are the hissing sounds /s/, /z/, /ʧ/ (as in 'catch'), /ʤ/ (as in 'judge', and /ʃ/ (as in 'wish').
It's probably less work in the long run to learn to distinguish voiced and voiceless sounds, so you only have to memorize two rules and five exceptions instead of long sound lists.
You can place a finger against the middle of your throat to feel for vibrations as a test for voiced sounds. Vibration = voiced sound, no vibration = voiceless. Eventually you'll learn to feel the vibrations in the throat itself without needing to place a finger.