Welcome to the community, Joey! :grinning_face_with_big_eyes: One thing to keep in mind is that the decimal and trailing zeroes that you see in 410.00 are due to display formatting. ARRAYJOIN isn’t rounding anything. What it’s collecting are the actual numbers, not their display-formatted versions. There’s no way to change this behavior, and no way to mass-reformat numbers inside an array.
You’ll need to use a formula to manually re-format the value, and then collect that manually-formatted version instead of the numeric value. I do this exact thing in one of my own bases, though this post prompted me to revisit my system, and I was able to optimize it a bit. In my actual base I use some helper formula fields as pseudo-variables to keep the main formula smaller, but here’s the full thing with all of that stuff in a single formula (replace references to Amount with your own value field):
Note that this is specifically optimized for currency display with a leading dollar sign. If you don’t want that, taking the dollar signs out of the formula may mess up the formatting depending on the value you feed it. You’ll need to wrap that full formula inside a SUBSTITUTE to remove it.
For another take on pretty-printing values like this, check out this thread and associated sample base by @W_Vann_Hall .
FWIW, the comma separation in a rollup is only cosmetic. That’s just how arrays are displayed. The commas aren’t actually in the data. If you want to separate each rolled-up item onto its own line, alter the ARRAYJOIN aggregation function to use a newline character (\n) as the separator: