I would do it the following way: All you need to do is to replace the Transaction table with whatever you have.
// ===== Some dummy transactions
rand() as Amount,
Date(round(MakeDate(2008) - 1 + 1000*rand())) as date
// ====== and a master calendar...
Set vFirstMonthOfFiscalYear = 4;
Load distinct *,
if(Month>FiscalMonth,Year & '/' & (Year+1), (Year-1) & '/' & Year) as FiscalYear;
Dual(Month,Mod(Month-$(vFirstMonthOfFiscalYear),12)) as FiscalMonth;
Year(date) as Year,
Month(date) as Month,
Date(MonthStart(date),'YYYY MMM') as RollingMonth