The solution which I presented just now works perfectly fine on the live editor of Matlab, but don't know why math works still say it is incorrect?
use fix instead of floor or ceil command
Test  Status  Code Input and Output 

1  Fail 
x = 8.8;
y_correct = 8;
assert(isequal(round_zero(x),y_correct))
x =
8

2  Fail 
x = 8.8;
y_correct = 8;
assert(isequal(round_zero(x),y_correct))
x =
8

3  Fail 
x = 0.8;
y_correct = 0;
assert(isequal(round_zero(x),y_correct))
x =
0

4  Fail 
x = 0.4;
y_correct = 0;
assert(isequal(round_zero(x),y_correct))
x =
0

5  Fail 
x = 0;
y_correct = 0;
assert(isequal(round_zero(x),y_correct))
x =
0

6  Fail 
x = eps;
y_correct = 0;
assert(isequal(round_zero(x),y_correct))
x =
0

7  Fail 
x = pi;
y_correct = 3;
assert(isequal(round_zero(x),y_correct))
x =
3

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