As per the list of groups in priority order in NCERT XI book carboxylic acid has highest priority. However in one of the books sulphonic acid group has been shown higher priority than carbocylic acid group.

The compound CH2COOH

                       CHCOOH

                       CH2COOH 

is named as propane-1,2,3-tricarboxylic acid.

The compound

HOOC-H2C-CH-CH2-CH2-COOH

                  CH2COOH

is named as 3-(carboxymethyl)hexanedioicacid.

Hope above examples would clear your doubt about using carboxy suffix.