This has been noted before on the forum.
https://forum.xojo.com/t/rounding-numbers/17100
MessageBox(Format(2.15, “0.0”)) → 2.1
MessageBox(Format(2.25, “0.0”)) → 2.2
MessageBox(Format(2.35, “0.0”)) → 2.4
MessageBox(Format(2.45, “0.0”)) → 2.5
MessageBox(Format(2.55, “0.0”)) → 2.5
MessageBox(Format(2.65, “0.0”)) → 2.6
The ensuing discussion attributed this behavior to the fact that things like 2.25 are actually Doubles and not exact.
“2.25 is stored as a Double, and is actually 2.24999(repeat), so it rounds down”
The discussion includes various strategies to get around this problem if it is important.