Prevent hundredths value from numeric field

Hello, 

I have a field (Hours), that should have entries that are whole numbers, or decimals in tenths of an hour (2.3). A lot of the time, users enter hundredths (2.25) instead. I don't want to automatically round, I just want to prevent the save from happening, and probably display a message like "Hours can only be entered in whole numbers or tenths of an hour". I thought using custom data rules might work, but I think I read somewhere that custom data rules aren't always reliable when users use grid edit, so I want to be sure whatever I do is 100% effective. Also, I need to prevent users from entering a value of 0; the # of hours should always be at least 0.1.​

If custom data rules would work, could someone provide a potential formula for this?

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Harrison Smith
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