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 $56.50   11.693%   $63.1065   $63.11   $63.10   $63.10  
  Purchase #2 $130.58   10.735%   $144.5978   $144.60   $144.60   $144.60  
  Purchase #3 $147.61   6.719%   $157.5279   $157.53   $157.55   $157.50  
  Purchase #4 $176.39   11.224%   $196.188   $196.19   $196.20   $196.20  
  Purchase #5 $83.53   11.172%   $92.862   $92.86   $92.85   $92.90  
  Purchase #6 $51.58   13.102%   $58.338   $58.34   $58.35   $58.30  
  Purchase #7 $224.59   10.302%   $247.7273   $247.73   $247.75   $247.70  
  7 purchase totals = $870.78       $960.3475   $960.36   $960.40   $960.30