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 $241.68   6.360%   $257.0508   $257.05   $257.05   $257.10  
  Purchase #2 $119.55   5.311%   $125.8993   $125.90   $125.90   $125.90  
  Purchase #3 $43.63   11.602%   $48.692   $48.69   $48.70   $48.70  
  Purchase #4 $184.71   10.692%   $204.4592   $204.46   $204.45   $204.50  
  Purchase #5 $97.68   5.817%   $103.362   $103.36   $103.35   $103.40  
  Purchase #6 $247.67   5.320%   $260.846   $260.85   $260.85   $260.80  
  Purchase #7 $15.58   10.462%   $17.21   $17.21   $17.20   $17.20  
  7 purchase totals = $950.50       $1,017.5193   $1,017.52   $1,017.50   $1,017.60