What the
is an ambiguous reference between means is that there are multiple references that match what you are requesting.
The solution is to determine which one you need to use and call it by its fully qualified name.
Try one or the other of these lines out; and see which one works out better for you
private static readonly ITaxEstimationService taxEstimationService = DIContainer.Resolve<Kadena.BusinessLogic.Contracts.ITaxEstimationService>()
private static readonly ITaxEstimationService taxEstimationService = DIContainer.Resolve<CMS.Ecommerce.ITaxEstimationService>()