四舍六入五成双 (9712)

C2=ROUND(B2,MAX(LEN(B2)-FIND(".",B2&"."),)-1)-(RIGHT(B2)="5")*(MOD(LEFT(RIGHT(B2,2+(LEFT(RIGHT(B2,2))="."))),2)=0)*10^IFERROR(FIND(".",B2)-LEN(B2)+1,1)