SQL error: function round(double precision, integer) does not exist

I received the following error when executing a SQL statement:

SQL error:
ERROR:  function round(double precision, integer) does not exist

In statement:

select id,smiles,smarts,parameter,oe_count_matches(smiles,smarts) as count,
round((parameter*oe_count_matches(smiles,smarts)),2)as psa,tpsa(smiles) as ctpsa,tpsa from structure,tpsa where id <
237610and oe_count_matches(smiles,smarts) > 0
 

order by id;

The functions described at:
http://www.postgresql.org/docs/7.4/static/functions-math.html
show that round(numeric,int) should work ok.
If I use round() without a second argument, it works OK, but
this gives a loss of precision which I do not want.

Can anyone help me with this?

Thanks,
TJ