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 $56.54   10.462%   $62.4552   $62.46   $62.45   $62.50  
  Purchase #2 $163.45   6.761%   $174.5009   $174.50   $174.50   $174.50  
  Purchase #3 $133.26   6.470%   $141.8819   $141.88   $141.90   $141.90  
  Purchase #4 $124.58   11.336%   $138.7024   $138.70   $138.70   $138.70  
  Purchase #5 $70.70   8.243%   $76.5278   $76.53   $76.55   $76.50  
  Purchase #6 $241.97   13.713%   $275.1513   $275.15   $275.15   $275.20  
  Purchase #7 $18.92   9.347%   $20.6885   $20.69   $20.70   $20.70  
  7 purchase totals = $809.42       $889.9080   $889.91   $889.95   $890.00