Owing on Taxes Again?!

I've done my 2011 taxes and this is the 3rd year in a row that I have owed. I cannot figure out why. I'm hoping you guys can give me some tips or some clarification as to why I am owing.

In 2011 I made about $29,000.

My main (basically full time) job takes off the proper amount of deductions. I know this because I check my pay stubs against the payroll deductions calculator on the Canada Revenue Agency website. It is always bang on.

My other part time job that I work at regularly also takes off the right amounts because they follow that same CRA calculator when they write my pay checks.

I did work a few random shifts at my old chain pharmacy job at 2 locations where they did not take tax off because I was making so little there. The income from those two places was only about $700 for the year. That's only $700 that I didn't pay tax on. I knew they were not going to take tax off so I made a point to try to contribute some money to RRSP's on my own to try to off-set that.

So I contributed $580.00 to RRSP's on my own.

It says I owe $133. I know I made a bit of extra money without paying taxes but even if I was to get a $700 pay check I would only pay about $45 in tax according to the CRA calculator. So what's the deal??

Any ideas?