What is the relation between IAS and TAS at a constant altitude?
If you divide 114/100 and 126/110 you'll find the common factor is ~1.14.

Which means for that altitude TAS ≈ 1.14 * IAS.

1.14 is the square root of the ratio of standard sea level ISA air density ($\rho_0$) to the air density at that altitude ($\rho$). This is assuming IAS = CAS = EAS (i.e., ignoring positioning, calibration, and compressibility effects).

The formula at low-speed flight is:

$$
\text{TAS}
=
\text{EAS}
\sqrt{
\frac{\rho_0}{\rho}
}
$$



It looks like you got the numbers from this online converter. Note its preset is not a standard ISA, as the altimeter setting reads 28.16 inHg. Instead I recommend this one, which is for standard ISA. For 5,000 ft the values are:

CAS    TAS
100    107.7
110    118.4
120    129.2


With the multiplier at 5,000 feet ISA being ~1.077, and the relation looks like this: