Well given the amount of time I spend in Zimbabwe (HRE)... infact my handle is even Zim**. It is interesting to note here, that in general no one tips anything. If you make $100usd a month you can actually survive, that is rent a place and eat the basics(talking starch and veggies here). Naturally that means you are poor. The highest paying companies pay no more than $4000 per month for individuals who are degreed lets say the 22-30 age bracket. Otherwise on average $1500 is the normal high. With a very select few making the $10k+ (maybe less than 3%) a month. Also remember that tax here is anything from 0% -55% depending on your bracket.
Now all those facts laid down, a taxi costs me $3 from point A to B and I have never tipped, felt pressured etc. Only places where there is any mention of tip are on slips from Holiday Inn, Crowne Plaza, and high end restaurants.
The logic is everyone else has factored the cost of service / wage into the salary however paltry it is.
Now if I go somewhere and I am extremely impressed I do tip. It is also usually more appreciated in the local pubs/bars to buy the bartender a drink as opposed to leave a tip, considered more friendly and the times I have asked the bartenders said they prefer to have a rapport with their clients and share a drink vs. the arggg he had to leave a $1.
my two cents