Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $73.65   11.616%   $82.2052   $82.21   $82.20   $82.20  
  Purchase #2 $136.98   12.556%   $154.1792   $154.18   $154.20   $154.20  
  Purchase #3 $106.46   6.720%   $113.6141   $113.61   $113.60   $113.60  
  Purchase #4 $125.47   8.865%   $136.5929   $136.59   $136.60   $136.60  
  Purchase #5 $217.93   5.411%   $229.7222   $229.72   $229.70   $229.70  
  Purchase #6 $176.25   10.873%   $195.4137   $195.41   $195.40   $195.40  
  Purchase #7 $148.77   4.492%   $155.4527   $155.45   $155.45   $155.50  
  7 purchase totals = $985.51       $1,067.1800   $1,067.17   $1,067.15   $1,067.20