Code for applying a discount to an order subtotal for nopCommerce 1.80:
http://www.mediafire.com/file/4wzl81v7p6rv5hy/Discount_Apply_to_Order_Subtotal.zip
Alternate download link:
http://www.mediafire.com/?4wzl81v7p6rv5hy
Archive includes:
-Instructions (INSTALL.txt)
-SQL query for new Discount Type
-modified/new files
DiscountTypeEnum.cs, ShoppingCartManager.cs, ShoppingCartManager_Mod.cs, & TaxManager.cs
-original unmodified files (in unmodified_original_files folder)
DiscountTypeEnum.cs, ShoppingCartManager.cs, & TaxManager.cs
-screenshot
INSTALL.txt includes instructions for unmodified version of 1.80 (replace existing files with new files) and for modified version of 1.80 (lists changes to make in modified files with line numbers of unmodified files -you may need to diff the files if you have changed any of the files).
.