void loop() {

scrollDigits();

}

Why? Having loop(), which is called in an endless loop() do nothing more than make a function call seems silly.

float voltage;

voltage = analogRead(voltPin);

voltage = (voltage / 1024) * 5.0;

voltage = voltage / denominator;

This could be done in one statement, with multiplication only, and no magic numbers, with a little forethought.

Store the value in an int, then, That will get you the whole number.

int wholeVoltage = voltage;

Then, subtract the whole number, multiply the rest by 100. Store the value in an int.

int fracVoltage = (voltage - wholeVoltage) * 100.0;

Then, add 5 and divide by 10.

fracVoltage += 5;

fracVoltage /=10;

If voltage was 3.262, wholeVoltage would be 3, and fracVoltage starts as 26, becomes 31, then become 3.