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 $67.37   13.614%   $76.5418   $76.54   $76.55   $76.50  
  Purchase #2 $97.56   5.522%   $102.9473   $102.95   $102.95   $102.90  
  Purchase #3 $163.32   13.563%   $185.4711   $185.47   $185.45   $185.50  
  Purchase #4 $45.38   3.796%   $47.1026   $47.10   $47.10   $47.10  
  Purchase #5 $24.55   13.547%   $27.8758   $27.88   $27.90   $27.90  
  Purchase #6 $76.63   5.796%   $81.0715   $81.07   $81.05   $81.10  
  Purchase #7 $231.30   8.145%   $250.1394   $250.14   $250.15   $250.10  
  7 purchase totals = $706.11       $771.1495   $771.15   $771.15   $771.10