This is the reason we recommend to
NEVER use February 29th as a "business day" - it makes comparative reporting a bear. Not only will you not pick up the February 29 transactions, but you'll get a date calculation error on February 29 since the date does not exist in the year prior.
To get the last day on ANY month, subtract 1 from the first day of the month following. Generally, you'll want to find out whether you are running a report on the last day of the month. Do that with:
IF MONTH(TODAY())+1 = MONTH(TODAY()) then
IF {SRW90 Transactions.Date} in LastYearMTD then
{SRW90 Transactions.Sales amount}
ELSE 0
ELSE
IF MONTH({SRW90 Transactions.Date})=MONTH(TODAY()) and
YEAR({SRW90 Transactions.Date})=YEAR(TODAY())-1 then {SRW90 Transactions.Sales amount}
ELSE 0