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 $249.67   4.691%   $261.382   $261.38   $261.40   $261.40  
  Purchase #2 $149.64   3.447%   $154.7981   $154.80   $154.80   $154.80  
  Purchase #3 $169.88   3.363%   $175.5931   $175.59   $175.60   $175.60  
  Purchase #4 $121.50   4.118%   $126.5034   $126.50   $126.50   $126.50  
  Purchase #5 $46.91   3.517%   $48.5598   $48.56   $48.55   $48.60  
  Purchase #6 $197.67   8.588%   $214.6459   $214.65   $214.65   $214.60  
  Purchase #7 $31.32   7.737%   $33.7432   $33.74   $33.75   $33.70  
  7 purchase totals = $966.59       $1,015.2255   $1,015.22   $1,015.25   $1,015.20