::Perhaps you could add an example, but good luck finding one where rounding isn't distinctive!  
 ::Actually, SOWL has two exaples. Nimboran [ki] 'woman', [kɨ] 'shit', [kɯ] 'day'. (You'd better get your vowels right in that language!) 
 ::Nweh (Ngwe) has a phonetic, though evidently non-phonemic distinction in [mbe] 'knife', [ntsə] 'water', [mbɤ] 'ivory'.