Round double down to nearest multiple of other double in Java?

I realize this isn't that great of a title, so I'll try to explain more thoroughly.

Basically, I have a double that changes only by small amounts, known as clusterSize. Then, I have a second double, a latitude or longitude on a map, known as coord. I want to round coord down to its nearest value that would be divisible by clusterSize, but we haven't found any easy way to do so.

Code tried:

private double roundDown(double coord, double clusterSize) {
    return clusterSize * Math.floor(coord / clusterSize);
}

And:

private double roundDown(double coord, double clusterSize) {
    return Math.floor((coord + clusterSize/2) / clusterSize) * clusterSize;
}

Neither of which produced the results that I was looking for. If you could point me to a library or function that could easily accomplish this task, that would be great. Thank you!