Hi Alcohol,
I work for a moving company in Singapore. For some reason customs do not always charge duty and tax on alcohol even when declared, but I wouldn't bank on this.
When declaring alcohol, sometimes your shipment will be selected by customs for inspection, which in itself incurs extra cost. Sometimes customs just assess duty/tax against shipper's declared list/values, therefore no inspection.
Full list of duties on link Volki shown. Opened bottles are normally considered full.
An example – One bottle of still wine, value S$30.00. Duty would be S$9.50. GST would be 3% of S$39.50. Therefore total duty/tax S$10.69.
Hope that helps.