Grand Total – Weird Behaviour

I have Advanced Product Fields and quantity discounts, rules and swatches installed on my shop.

The Grand Total amount works as it should when that specific product isn’t yet in the cart. However, if I add it to the cart and then try to add that product again, the Grand Total amounts don’t make any sense? They are correct when you go to view the cart but aren’t in the Grand Total section.

For instance, with the variables I have, when you are adding 100 bands to cart they are £100 total, if you want to add 250 bands they are now £150 total because of tiered pricing.

However, if I add that to cart and then try to add the same product to cart again with different options (that cost the same) – any amount of product below 250 stays stuck at £100 total, and if I then change to 250 quantity it goes down to £60 total.

Are you able to help?

Thanks

The page I need help with: [log in to see the link]