in a restaruant usually about 10 to 15 per cent of total cost IF the service has been very good . if not then it is up to your discretion.
taxi drivers and hotel staff i would normally give 2 to 5 dollars if , again , the service was good , they were freindly and polite, although i do not like to be called sir all the time.this is just me and every body is different.
at the end of the day you do not have to tip them , they are doing their chosen job. i do not expect to get a tip when i do a delivery.
if they dont like it , then tough , sorry to say. 
