Saying "we're at 5,043.25" is slow. Traders say "43 handle" or "we lost the 5,000 handle" and everyone knows the ticks are implied. In bonds the handle is the whole point and the fraction is quoted separately in 32nds.
Round handles attract orders for no reason other than that they are round, which is why stop clusters and support reactions gather at 50- and 100-point figures.
Example: ES trading 5,042.75 to 5,043.50 is "the 43 handle". A trader who says "I'll buy the 5,000 handle" means anywhere in 5,000.00 to 5,000.75.
Related: tick-size, support, resistance, es