SQL join two tables by modifying on columns

I have 3 tables on PostgreSQL:

SPENDINGS:

store      |spending
-----------+---------
0000700551 |   $75

STORE:

store  | zip_code
-------+---------
700551 | XXP PDD

CUSTOMER:

id  | zip_code
----+----------
002 | XXPPDD

I would love to join these tables like this:

right(SPENDIGNS.store, 6) = STORE.store and     
trim(STORE.zip_code) = CUSTOMER.zip_code.

How can I do that could you help me out please?

Answer

trim(store.zip_code) is not good for the job because the whitespace is within the zip code text. Use replace(store.zip_code, ' ', '') instead. right(spendings.store, 6) does not seem safe to me too. Better use ltrim(spendings.store, '0') to remove leading zeroes. SQL Fiddle

select * 
  from spendings sp 
  join store st on ltrim(sp.store, '0') = st.store
  join customer cu on cu.zip_code = replace(st.zip_code, ' ', '');

BTW your data design does need improvement.