So let's see...

@Amazon.com...
Stargate UE : 14.99
X-Men 1.5 : 17.54
Road to Perdition (DTS Widescreen) : 20.24

Without STL
Total: 14.99 + 17.54 + 20.24 + 3.99 + 2.49*3 - 5 = US 59.23 = NT 2073

So in effect, Stargate UE is NT 600, X-Men 1.5 is NT 689, Road to Perdition is NT 784

With STL
Total: 0.9 *( 14.99+ 17.54+ 20.24) +3.99 + 2.49*3 - 5 = US 53.95 = NT 1888

So in effect, Stargate UE is NT 548, X-Men 1.5 is NT 628, Road to Perdition is NT 721

@Amazon.ca
Stargate US : 19.59
X-Men 1.5 : 29.60
Road to Perdition (DTS Widescreen) : 29.61

Total: 19.59 + 29.60 + 29.61 + 4.99 + 2.49*3 - 5 = CDN 86.26 = NT 1940

So in effect, Stargate UE is NT 497, X-Men 1.5 is NT 721, Road to Perdition is NT 722

Therefore, if you can get STL, it would be a good deal to get all three at Amazon.com. Otherwise, Amazon.ca still has an edge

I must stress that buying all three on one order is not a good idea because we can get the most out of our $5 coupon if we just buy 2 (for example, the total is US 35.23 for Stargate UE & Road to Perdition)

If we only get Stargate UE and Road to Perdition (DTS WS)

@Amazon.com...
Stargate UE : 14.99
Road to Perdition (DTS WS) : 20.24

Without STL
Total: 14.99 + 20.24 + 3.99 + 2.49*2 - 5 = US 39.2 = NT 1372

So in effect, Stargate UE is NT 594, Road to Perdition is NT 778

With STL
Total: 0.9 *( 14.99+ 20.24) +3.99 + 2.49*2 - 5 = US 35.68 = NT 1249

So in effect, Stargate UE is NT 542, Road to Perdition is NT 707

@Amazon.ca
Stargate US : 19.59
Road to Perdition (DTS Widescreen) : 29.61

Total: 19.59 + 29.61 + 4.99 + 2.49*2 - 5 = CDN 54.17 = NT 1219
So in effect, Stargate UE is NT 497, Road to Perdition is NT 722

In summary, Stargate UE is NT 497 at Amazon.ca if your order has 2 or 3 DVDs. At Amazon.com, Stargate UE is at least NT 542. On the other hand, the other 2 DVDs are cheaper at Amazon.com, especially if you have STL.