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 $127.59   7.716%   $137.4348   $137.43   $137.45   $137.40  
  Purchase #2 $103.51   12.503%   $116.4519   $116.45   $116.45   $116.50  
  Purchase #3 $184.78   11.439%   $205.917   $205.92   $205.90   $205.90  
  Purchase #4 $34.79   9.840%   $38.2133   $38.21   $38.20   $38.20  
  Purchase #5 $198.25   7.356%   $212.8333   $212.83   $212.85   $212.80  
  Purchase #6 $64.98   10.357%   $71.71   $71.71   $71.70   $71.70  
  Purchase #7 $18.67   6.242%   $19.8354   $19.84   $19.85   $19.80  
  Purchase #8 $14.96   7.467%   $16.0771   $16.08   $16.10   $16.10  
  Purchase #9 $65.98   5.557%   $69.6465   $69.65   $69.65   $69.60  
  Purchase #10 $127.37   8.594%   $138.3162   $138.32   $138.30   $138.30  
  10 purchase totals = $940.88       $1,026.44   $1,026.45   $1,026.30  
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?