Look:

A = 11.531681447264651 B = 10.276344990825836 C = 0.11732116415316027 D = 10.7

Now, try it:
A - B -C*D

Result: 6.661338147750939e-16

1. Why a result so small?

But, lets round it:
round(A,1) - round(B,1) -round(C,1)*round(D,1)

Result: 0.12999999999999923
Great result! If a try in calculator

11.5 − 10.3 −0,1×10.7 = 0.13

2. Why 6.6e-16 before and now 0.129999 ?

Other thing weird:
round(A,2) - round(B,2) -round(C,2)*round(D,2)

Result: -0.03399999999999981

3. Why negative now?

4. My experimental results is with precision 1, so, should I put all A, B and C numbers to precision 1 before do this math, right?

I tried all variations, and solved using round(x,my_precision) before the math, but I would like to understand what is happening