Let's do some math ..  Rounding examples of 10 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $179.42   5.799%   $189.8246   $189.82   $189.80   $189.80  
  Purchase #2 $115.36   4.177%   $120.1786   $120.18   $120.20   $120.20  
  Purchase #3 $123.28   5.233%   $129.7312   $129.73   $129.75   $129.70  
  Purchase #4 $229.38   5.236%   $241.3903   $241.39   $241.40   $241.40  
  Purchase #5 $106.36   5.831%   $112.5619   $112.56   $112.55   $112.60  
  Purchase #6 $226.64   11.445%   $252.5789   $252.58   $252.60   $252.60  
  Purchase #7 $248.59   13.325%   $281.7146   $281.71   $281.70   $281.70  
  Purchase #8 $220.71   7.438%   $237.1264   $237.13   $237.15   $237.10  
  Purchase #9 $139.41   10.462%   $153.9951   $154.00   $154.00   $154.00  
  Purchase #10 $150.29   12.796%   $169.5211   $169.52   $169.50   $169.50  
  10 purchase totals = $1,739.44       $1,888.62   $1,888.65   $1,888.60  
Come on folks.. this just does not make any cents. We got rid of the 1/2 cent back in 1857.. Getting rid of the 1 cent coin is way, WAY past due. The penny has become a social and cultural anachronism. If our friends in Canada, Australia and a dozen other countries can stop the use of their pennies, why can't we?