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 $56.35   12.778%   $63.5504   $63.55   $63.55   $63.60  
  Purchase #2 $187.40   8.208%   $202.7818   $202.78   $202.80   $202.80  
  Purchase #3 $217.71   5.178%   $228.983   $228.98   $229.00   $229.00  
  Purchase #4 $93.59   5.488%   $98.7262   $98.73   $98.75   $98.70  
  Purchase #5 $244.93   6.559%   $260.995   $261.00   $261.00   $261.00  
  Purchase #6 $118.93   5.283%   $125.2131   $125.21   $125.20   $125.20  
  Purchase #7 $241.94   6.455%   $257.5572   $257.56   $257.55   $257.60  
  7 purchase totals = $1,160.85       $1,237.8067   $1,237.81   $1,237.85   $1,237.90