What is 2.25 L rounded to nearest tenth?

It is 2.2 L.

Although many schools teach you to round 5 up, always rounding up from 5 is inappropriate because it introduces an upward bias. The IEEE (Institute of Electronic and Electrical Engineers) standard 754 is to round 5 up or down so that the new last digit is even. See link for more: //en.wikipedia.org/wiki/Rounding#Round_half_to_even