You're not wrong...the markup and/or commission on third party lenses is
higher, and the Tamron isn't that great of a performer.

For macro shots, you typically want a 1:1 reproduction ratio, and
usually a prime lense. The Tamron offers neither.

Do you have a budget?

For about twice the price and 10x the optical quality, take a look at
the Nikon offering:

http://www.nikonimaging.com/global/products/lens/af/micro/af_micro60mmf_28d/index.htm

http://www.bythom.com/105AFSlens.htm

Thom Hogan reviews the 105mm f/2.8 VR micro-Nikkor here, but at the end
of the review he talks about the Tamron 90mm f/2.8 Di. You might want
to take a look at that instead.

Unless your budget can't afford better, I would avoid it.   Tamron makes some
decent lenses, but that is not one of them.  In fact, no 70-300 is.  If you
need a 70-300, consider the Nikon ED version, as at least it is branded as
Nikon and will resell better if you upgrade later [it is also widely rumored
to be made by Tamron anyway ... but I wonder].

I like to buy Nikon lenses as my first choice, but consider others
occasionally.  I am especially impressed by Tokina.

If you are truly interested in close ups, skip the zooms.. period.  Get
a prime.  Nikon makes some of the best macro (Nikon Micro) lenses in
the business..    I would stick with the Nikon 105mm f/2.8G ED-IF AF-S
VR Micro-Nikkor or even a used Nikon 105 AF Micro if you can't afford
the new one.  For close ups, seriously, ignore the macro on any zoom.  
There are just two many comprises made in the lens design to give you
any real credible close up on a zoom macro lens.

I initially bought the Nikon 70-300mm f/4-5.6 G lens for my D70s, but I
wasn't totally happy with this lens in low light.

So, I picked up a used Nikon 80-200mm f/2.8 lens and I am extremely
happy with it for close up photography.  It is an amazing piece of
glass for the money.

My advice, for anyone purchasing the D70 or D70s camera, is to buy at
least one really good lens for it.  The best bargain for the dollar is
the 50mm f/1.8 prime lens.

---------------------

What kind of close-ups?  Portraits?  Macros?

A great lens that does both well is:

Nikon 105mm f/2.8D

Unless you have an unlimited budget, don't worry about the VR model of
this.  The f/2.8D is superb.  Check out deals on used models.  I picked
up an absolutely pristine example a couple months ago for $418 via
eBay.

Kevin

Enter the cheap guy.. me.  I have the lens you ask about and actually
it's not bad for closeups from a distance, not macro, but closeups.  I
got it almost by accident while bidding on a D50 body that happened to
include the Tamron and Nikon kit lens at such a low price I couldn't
resist.  I intended to sell it, but hung onto it as the result of some
good insect and bird closeups I've snagged with it.  I'd say it does as
good a job as the Nikon 70-300G lens which I also have.  Neither are
perfect by a long shot, but okay on a monopod in decent light.

Now, the real reason for my post.  Get a copy of the
Phoenix/Vivitar/(and a couple other names) 100mm macro.  I think I paid
about $120 for the autofocus version and it's really a dandy little
lens if you don't do a lot of macro photography.  It might keep you
from spending $400 to $1000 and more on a lens you don't really need
and won't use much.  Yes, it's a cheap plastic lens.  Yes, the
autofocus is noisy.  But, it takes some dandy closeups at it's native
1:2 and with the screw on diopter, it will do 1:1.  It is unbelievably
sharp for something this cheap.  I'll probably get flamed for my
heresy, but root around the internet a little and I think you'll find
others who like this little plastic wonder as well as I do.  Anyway,
the price is right and if you decide macro is for you, you can always
sell it for a few bucks and get one of the big guns.

I found a link to a review if you're interested:

http://www.nikonians.org/html/resources/non-nikon_articles/phoenix/100f35-1.html

If you mean tele, not macro, then:
Nikon 70-300/4.5-5.6 VR
Nikon 180/2.8

http://digitcamera.tripod.com/#slr