if there is a tie ----- is it a push

Depending on the wager. Straignt bets YES its a push.

Depends on the sport and the bet chosen.

No

I've done standard parlays and received an adjusted payout. If you want to buy points (most sports) they only allow them to be half points. So if the Nets are +3 and you want to buy points you can buy .5(+3.5) 1.5(+4.5) 2.5(+5.5) and so on, this obviously eliminates the possibility of a push.