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 $141.73   10.464%   $156.5606   $156.56   $156.55   $156.60  
  Purchase #2 $145.31   13.318%   $164.6624   $164.66   $164.65   $164.70  
  Purchase #3 $86.35   7.383%   $92.7252   $92.73   $92.75   $92.70  
  Purchase #4 $65.81   6.242%   $69.9179   $69.92   $69.90   $69.90  
  Purchase #5 $197.49   5.162%   $207.6844   $207.68   $207.70   $207.70  
  Purchase #6 $137.56   12.353%   $154.5528   $154.55   $154.55   $154.60  
  Purchase #7 $60.63   10.774%   $67.1623   $67.16   $67.15   $67.20  
  7 purchase totals = $834.88       $913.2656   $913.26   $913.25   $913.40