Automatically extract numbers divisbible by 10 wholly

I Have attached a screenshot for understanding.

I have a sheet of investment plan.

The condition is investment can only be made at multiple of 10s (Eg 200, 210, 220, 230, 240, 250).
Investments cannot be made in decimals or in number which is not wholly divisible by 10 (Eg 204.5, 205 , 208.9)
Eg:
Original Investment was $324
But I can only invest $320 (324 it is not divisible by 10)
I earned at 7 %. Therefore, (320*7%=22.4)
Revised Investment = 324 + 22.4= 346.40

Now, next time I can invest is only $340 and not $346.40 (6.40 cannot be invested)
My question is How I can automate this "Invested number in excel" i.e (if it is 324, excel automatically gives 320 and if it is 345.54 excel automatically gives me $345.


I have also attached excel file for reference. This sheet is made manually as it is difficult to ascertain formula.