Square of no having unit digit 5

Square of no. having unit digit is 5 can be found by adding 1 to the no except unit digit i.e. 5 and multiply this no to the original no. in which we can add 1 and finally write the 25 in the last of the digit
5^{2}=25
15^{2}=(1)(1+1) 25=1 2 25 =225 ;
25^{2}=(2) (2+1) 25=2 3 25=625 ;
35^{2}=(3) (3+1) 25=3*4 25=1225 ;
then find ;
605^{2}