I think with my use case it is imperative that where no variables have changed then each day must have the same amount. When reporting (using an SSAS cube) each daily amount will look the same (however they are rounded they will all be rounded the same way), and the total will be correct (the total of all the floats). Although if someone tries to sum the rounded figures they will likely get a different total to that given by the cube - but then why would they do that?.
I think in your example with reporting I would rather see 3 amounts of 333.33 (rounded from the float), rather than one day that has 333.34 - surely that suggests a different amount on that day?
Generally I think I should store to the best precision possible (float).
Thanks for your input.