DAX code
Total Sales (K/M/B) =
VAR Value = [Total Sales]
RETURN
SWITCH(
TRUE(),
ABS(Value) >= 1000000000, FORMAT(Value / 1000000000, "#,##0.0") & "B",
ABS(Value) >= 1000000, FORMAT(Value / 1000000, "#,##0.0") & "M",
ABS(Value) >= 1000, FORMAT(Value / 1000, "#,##0.0") & "K",
FORMAT(Value, "#,##0")
)