Keep k+ties largest elements in a stream
Keep a binary heap, where each element in the heap is a unique key value together with a pointer to a list of all the items with that key value.

For instance, with the input list $[10,5,7,5,7,9,10]$, the unique key values are $5,7,9,10$, so you'd have a heap containing the following 4 elements: $5$ (with a pointer to the list $[5]$), $7$ (with a pointer to the list $[7,7]$), $9$ (with a pointer to the list $[9]$), and $10$ (with a pointer to the list $[10,10]$).  Now you can find the top-$k$ elements (with ties) straightforwardly using this heap data structure.