Buzzer tip for quick answer at end of quiz rounds (5)
I believe the answer is:
kazoo
'buzzer' is the definition.
(instrument making a buzzing sound)
'tip for quick answer at end of quiz rounds' is the wordplay.
'tip for' says to take the final letters (one tip of the word).
'answer' becomes 'a' (abbreviation eg in Q and A).
'at end of' indicates one should take the final letters.
'rounds' becomes 'oo' (two O's - O is a round letter).
The final letter of 'quick' is 'k'.
The last letter of 'quiz' is 'z'.
'k'+'a'+'z'+'oo'='KAZOO'
(Other definitions for kazoo that I've seen before include "Toy wind instrument that buzzes" , "Humming toy" , "Toy-like instrument into which one hums" , "Simple musical instrument" .)