In Business Central, in the Currency table, in the Amount Decimal Places and Unit Amount Decimal Places fields, you can set up the minimum and maximum number of digits to use when formatting a decimal number. This is also known as Auto Format.
To enforce this in FORNAV, you must specify the Currency Code field on the data item, so FORNAV will pick the currency code and look up the decimal places for the Amount and Unit Amount values from the Currency table.
Additionally, for the controls where you want to use Auto Format, you must specify if you want to use the Amount or Unit-Amount decimal places to do the formatting.