JMP Numeric Formats change the way data appears, but not the underlying value. Probably you need the 'Round()' function, but as always, you should be cautious in modifying the data values themselves. Copy and paste the code below into a script window, do 'Edit > Run Script', then look at the formula columns:
New Table( "Formats and Rounding",
Add Rows( 10 ),
New Column( "Precise Value",
Numeric,
"Continuous",
Format( "Best", 12 ),
Formula( Random Normal() )
),
New Column( "Precise Value with 'Fixed Dec' Format",
Numeric,
"Continuous",
Format( "Fixed Dec", 12, 2 ),
Formula( :Precise Value )
),
New Column( "Precise Value with 'Precision' Format",
Numeric,
"Continuous",
Format( "Precision", 12, 2 ),
Formula( :Precise Value )
),
New Column( "Precise Value Rounded to 2 Decimal Places",
Numeric,
"Continuous",
Format( "Best", 12 ),
Formula( Round( :Precise Value, 2 ) )
)
)