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 $91.42   13.226%   $103.5112   $103.51   $103.50   $103.50  
  Purchase #2 $5.42   13.603%   $6.1573   $6.16   $6.15   $6.20  
  Purchase #3 $35.99   10.275%   $39.688   $39.69   $39.70   $39.70  
  Purchase #4 $245.52   6.385%   $261.1965   $261.20   $261.20   $261.20  
  Purchase #5 $208.97   12.400%   $234.8823   $234.88   $234.90   $234.90  
  Purchase #6 $46.37   10.851%   $51.4016   $51.40   $51.40   $51.40  
  Purchase #7 $91.95   6.486%   $97.9139   $97.91   $97.90   $97.90  
  7 purchase totals = $725.64       $794.7508   $794.75   $794.75   $794.80