Math.floor? Round Down to Nearest 10th

Hi Folks, Math is not my friend so I need some help.

I want to round a whole number down to the nearest whole 10th.

Like 52, becomes 50. Or 49, becomes 40. Or 2005, becomes 2000.

Does that make sense? I imagine it has a math.floor approach, but I can not figure it out.

Thanks in advance for any help!!!