To round off a number to nearest thousands,

If the number at hundred place is 0, 1, 2, 3 or 4 we round down

If the number at hundred place is 5, 6, 7, 8 or 9 we round up.

5, 001 on rounding off to nearest thousands gives 5000

(since at hundred place is 0)

5, 559 on rounding off to nearest thousands gives 6000

(since at hundred place is 5)

5, 999 on rounding off to nearest thousands gives 6000

(since at hundred place is 9)

5, 499 on rounding off to nearest thousands gives 5000

(since at hundred place is 4)

Thus the number which rounds off to 5000 and is the largest is 1 less than 5000

= 5000-1

= 5499