There are approximately 94.5 water bottles in a gallon, or 2,840 mL in a gallon.
This isn't too complicated to figure out - just divide the number of water bottles by the number of milliliters per bottle! It should be easy to get to 2,880 mL/oz if it's not already there :)
The main issue with change is how it's perceived. For instance, many people will perceive dollar bills as being more valuable because they come from a larger currency so smaller denominations can appear cheap by comparison even though they're worth similar amounts. It's common these days for retailers and even thieves to keep count in dollars but use cents when asking for change or giving receipts because it makes sense psychologically.