Yeah this is exactly what I do under the hood. All the data is stored as Ints, charts use double for speed, views use decimal to display stuff properly in the user locale.
P.S. Doubles are absolute evil for calculations:
@Test
func test() {
var a = Decimal(100.4449315513924) * 100 // It's me being dumb, not noticing that
let b = NSDecimalNumber(decimal: a).intValue
#expect(b == 10044) // Expectation failed: (b → -8402) == 1044
}