The Currency Format is a very attractive format to use. You do not have to bother with rounding off to two decimal places nor do you have to bother with the $ or £ or ¥ or... symbol. Access does it all for you. Since everything is so fantastic and ready-to-use and user-friendly, what's the catch you wonder?
Well, using the currency format for amount fields in your forms 'hard codes' the currency format specified in your OS settings. So if you are an off shore developer you need to be doubly careful about currency settings. Not just that, if you are developing a multi-currency system, this will not work at all. Other than that, the rounding off is not very reliable and we have found that it is always safer to use a Double format for amounts. And do the extra work of putting the currency symbol before / after the amount.
As usual, we learnt this the hard way!!