Look up Psalm 56:8. While God may not keep all of our tears, He keeps the tears that we cry when we are truly repenting as shown in 2 Kings 20:5 and Malachi 2:13. In Job 16:20, we see that God keeps our tears that we cry in sorrow. In Ester 8:3, we see that God will keep our tears when we are trying to do what is right. In Psalm 126:5-6, we see that God both keeps our tears that we cry when trying to witness to someone and also we will reap benefits from that. In Psalm 6:6, we see that God keeps our tears that we cry in grief.