Applying a macro to all worksheets in workbook

Hi.

I am currently working on a loan amortization table. I'm getting some rounding errors in some of my values and i was wondering if anyone knew how to eliminate these.

I was also wondering how i would go about applying the following to all the worksheets in the workbook?

Sub testing()

Dim myVariable As Long
myVariable = Range("E" & Rows.Count).End(xlUp).Row
Sheet1.Range("J8") = "=Sum(E19:E" & myVariable & ")"

End Sub

thanks in advance!