May 31, 1981 or prior $7.40
June 1, 1981 and May 31, 1982 $8.60
June 1, 1982 and May 31, 1985 $10.00
June 1, 1985 and May 31, 1986 $10.50
June 1, 1986 and May 31, 1987 $11.00
June 1, 1987 and May 31, 1988 $11.50
June 1, 1988 and July 31, 1990 $12.00
August 1, 1990 and July 31, 1991 $14.00
August 1, 1991 and July 31, 1992 $16.00
August 1, 1992 and July 31, 1993 $18.00
August 1, 1993 and July 31, 1994 $20.00
August 1, 1994 and January 31, 1995 $22.00
February 1, 1995 and June 30, 1995 $24.00
July 1, 1995 and June 30, 2003 $30.00
July 1, 2003 and June 30, 2004 $34.00
July 1, 2004 and June 30, 2005 $38.00
July 1, 2005 and the present $40.00