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 $136.96   5.440%   $144.4106   $144.41   $144.40   $144.40  
  Purchase #2 $17.62   9.107%   $19.2247   $19.22   $19.20   $19.20  
  Purchase #3 $65.34   13.141%   $73.9263   $73.93   $73.95   $73.90  
  Purchase #4 $247.64   5.427%   $261.0794   $261.08   $261.10   $261.10  
  Purchase #5 $40.55   10.221%   $44.6946   $44.69   $44.70   $44.70  
  Purchase #6 $188.69   12.638%   $212.5366   $212.54   $212.55   $212.50  
  Purchase #7 $36.51   5.621%   $38.5622   $38.56   $38.55   $38.60  
  7 purchase totals = $733.31       $794.4344   $794.43   $794.45   $794.40