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 $105.99   6.817%   $113.2153   $113.22   $113.20   $113.20  
  Purchase #2 $95.65   6.340%   $101.7142   $101.71   $101.70   $101.70  
  Purchase #3 $67.90   5.257%   $71.4695   $71.47   $71.45   $71.50  
  Purchase #4 $182.37   8.779%   $198.3803   $198.38   $198.40   $198.40  
  Purchase #5 $76.29   10.649%   $84.4141   $84.41   $84.40   $84.40  
  Purchase #6 $97.38   9.584%   $106.7129   $106.71   $106.70   $106.70  
  Purchase #7 $113.85   4.225%   $118.6602   $118.66   $118.65   $118.70  
  7 purchase totals = $739.43       $794.5665   $794.56   $794.50   $794.60