How to add numbers to a position when controlling a seven-segment display
In your code, you call:

newPos = encoder.getPosition();


which grabs the absolute position of the encoder. When you rotate this one step, the value of newPos goes up (or down) by one.

Then, you make pos = newPos + 4, which simply adds 4 to the value that is going up or down by one step at a time.

newPos: 1    pos: 5
newPos: 2    pos: 6
newPos: 3    pos: 7
newPos: 4    pos: 8
newPos: 5    pos: 9


Instead, it sounds like you wish the display to always read 5 times the encoder position. If so, then you should write pos = newPos*5.

newPos: 1    pos: 5
newPos: 2    pos: 10
newPos: 3    pos: 15
newPos: 4    pos: 20
newPos: 5    pos: 25


Then, when you write to the display, you do so as:

display.showNumberDec(newPos, true); // Expect: 1234


But newPos is not the newly calculated value. Instead, call

display.showNumberDec(pos, true); // Expect: 1234