SQL & PL/SQL

Because of the large decimal places in my percent column when I try to simply multiply the percent times the amount paid the net result ends up with an extra penny. I'm trying to write a query to keep track for the subtraction in a separate column. In that way I can simply distribute the difference to the last amount. Here is what I have so far.

CREATE TABLE MY_TEST 
   ( USER_ID VARCHAR2(600 BYTE), 
USER_DETAIL_CODE VARCHAR2(100 BYTE), 
DETAIL_CODE VARCHAR2(4 CHAR) NOT NULL ENABLE, 
PERCENT NUMBER(8,5), 
USER_AMOUNT_PAID NUMBER, 
WORKING_PERCENT NUMBER
   )

Insert statement.

REM INSERTING into MY_TEST
SET DEFINE OFF;
Insert into MY_TEST (USER_ID,USER_DETAIL_CODE,DETAIL_CODE,PERCENT,WORKING_PERCENT,USER_AMOUNT_PAID) values ('POP','F821','F821',7.14,0.0714,150);
Insert into MY_TEST (USER_ID,USER_DETAIL_CODE,DETAIL_CODE,PERCENT,WORKING_PERCENT,USER_AMOUNT_PAID) values ('POP','F821','F821',10.47,0.1047,150);
Insert into MY_TEST (USER_ID,USER_DETAIL_CODE,DETAIL_CODE,PERCENT,WORKING_PERCENT,USER_AMOUNT_PAID) values ('POP','F821','F821',62.39,0.6239,150);
Insert into MY_TEST (USER_ID,USER_DETAIL_CODE,DETAIL_CODE,PERCENT,WORKING_PERCENT,USER_AMOUNT_PAID) values ('POP','F821','F821',20,0.2,150);

.

the running subtraction column is simply subtracting (10.71 - 150) which equals 123.58 than (139.29 -15.71) than (123.58 -93.59)

my goal is to essentially replace the 30 with 29.99 since otherwise my summation is of by .01 .

SELECT
    user_id,
    user_detail_code,
    detail_code,
    percent,
    user_amount_paid,
    working_percent,
    round((working_percent * user_amount_paid),2) paid_times_percent,
    ''running_subtraction
FROM
    my_test;

I've written the above query but I just can't seem to come up with the right syntax for the running subtraction.

Any help would be appreciated.