Can capital gains tax be rolled over

Can you explain what you mean?  Are you asking about the possibility
of offsetting capital gains and losses from different years?

If you are talking about real estate, then yes. A 1031 exchange will
transfer any equity into new piece of real estate (of a similar type)
tax free. The only time you will pay tax is if you don't tranfer all
of the equity (and keep some) or when you sell the second property in
the future.

This depends on:

- which country you are in

- the circumstances of the gain

- what you are buying (if anything) with the proceeds

A capital loss can be rolled over for tax purposes to offset a future
gain i think.. but of course it depends on country/item/etc