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 $67.40   13.280%   $76.3507   $76.35   $76.35   $76.40  
  Purchase #2 $209.26   10.818%   $231.8977   $231.90   $231.90   $231.90  
  Purchase #3 $246.33   6.255%   $261.7379   $261.74   $261.75   $261.70  
  Purchase #4 $111.51   8.126%   $120.5713   $120.57   $120.55   $120.60  
  Purchase #5 $32.70   8.642%   $35.5259   $35.53   $35.55   $35.50  
  Purchase #6 $119.92   13.452%   $136.0516   $136.05   $136.05   $136.10  
  Purchase #7 $102.69   12.400%   $115.4236   $115.42   $115.40   $115.40  
  7 purchase totals = $889.81       $977.5587   $977.56   $977.55   $977.60