How to round to 0, 5 or 9 which ever is closest?

Are you referring to the first decimal digit, the units digit, or the number itself?  How do you deal with "ties" (round up or down)?  For example, to what would you want 10.7 rounded?  I could imagine 10.5, 10.9, or 9 depending on your other rules.

To the number itself, 10.7 should be just a 10

If you wanted to round the number itself, you'd round to 9,  10 wasn't in the list of rounding.  Are you referring to the units digit (the "0" in "10")?  If so, to what would you want 7 rounded?

Up to a 9

This could be done with a complex Choose function or with VLookup.  The key is to separate off the units digit, decide if it should be 1, 5, or 9 (using Choose or VLookup), then replace the units digit of the original number with the new digit.
int(number) - Mod (number,10) will give you the digit with which to work, call it unit
choose(unit, 0,0,0,5,5,5,5,5,9,9) will give you 1, 5, or 9 (I assumed you want 7 to return 9), call it NewUnit
Mod (number,10) + NewUnit will give you the result

I was incorrect.  My assumption was to change 7 to 5, not 9.  To change 7 to 9 use: choose(unit, 0,0,0,5,5,5,5,9,9,9)

You could wrap those three lines into one (rather ugly!) statement if you wish.

This is for Google Spreadsheets?

Don't know.  I saw "spreadsheets" and assumed Excel.

I would hope that Google spreadsheets had something similar.