If you are keeping 1.4 as a double, the math routines will treat it as 1.4 no matter how many 0's are at the end of if.
If you are printing/displaying 1.4 as a string, try just a simple string append:
Dim n As Double = 1.488
Dim m As Double = Floor(n*10)/10
Dim s As String = m & "0"
BTW, In Excel 2007, TRUNC(1.488,1) returns 1.4