LEDs are pretty forgiving. It also depends if you want it bright or dim. Dimmer can make an LED last forever. It is not important what the operating current is as long as you don't exceed the max rating, and you have a DVM with current input to monitor it while you experiment.
Im not sure about your math: most LEDs are 3V devices @ 20-30ma without a dropping resistor. At 5V, you should use a 100 ohm reisitor minimum [50ma], up to 500 ohm [10ma] depending on how bright you want it [ohms law: 5/100=50, 5 divided by 100 = 50].
For automotive use, you want to plan on 10-14.8V [15V max] because the voltage fluctuates a lot in a car system. So you would start with a 300 ohm resistor [2200ma @ 15V=bright], up to 2K [7.5ma=dim] to throttle it down some, or somewhere in between =1K to allow a wide range of voltage to be tolerated by the LED.
These high-bright LEDs can go up to 70ma so even 80 ohms @ 5V, and 220 ohm @ 15V would work for MAX brightness.
To learn how this works, set up on your bench using a 5K ohm potentiometer and goof around with it, measuring the current thru a DVM. Have fun!