How to select standard resistor values for a voltage divider?
Yes, there are online calculators that will allow you to find resistor pairs that will closely approximate the desired ratio. For example, this one.
If you wanted to have (say) 3.0V out and your reference is 0.8V and we're ignoring bias current, and we're using E96 series (1%) values we get the following results:

Obviously you can scale the values by decades up or down, for example you could use 1.18K and 3.24K.
This particular calculator (and some others) works well in this case because we're not overly concerned with the total resistance of the divider.
Note that a 0.108% (for example) error in the nominal values is dwarfed by the 1.47% worst-case error due to resistor tolerances.
You can also do it manually, takes a bit longer, but just try values from the E96 table and find the closest pair.
And if you really want to hit the nominal values virtually bang-on you can add a resistor series or parallel to one of the pair. That may not be as bad it seems because you can probably pick two of the three resistors as values that you are already stocking, have a reel of, etc. and only one &quot;weird&quot; value is required.
As with anything else online, best pull your your calculator or fire up a spreadsheet and double-check the numbers for yourself.