Decimal precision in an EXTJS grid

Decimal precision in an EXTJS grid

I have a grid which lets a user enter in a number by editing the row. I
want the number to support 4 decimal places, but it only supports 2. I
figured out how to display 4 decimal places but it doesn't register
anything more than 2 decimal places.
So if the user enters 1000.1111 the resulting field will show 1000.1100 in
the grid. How can I tell the model that the field is precise to 4 decimal
places?
My field in the model looks like this: {name: 'Price_Customer__c', type:
'number'},
The column in the grid is set up like this: { header: 'Price to Customer',
flex: 0, width: 100, sortable: true, renderer:
Ext.util.Format.numberRenderer('$0,000.0000'), dataIndex:
'Price_Customer__c', summaryType: 'sum', field: { xtype: 'numberfield' }
},