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 $232.48   12.567%   $261.6958   $261.70   $261.70   $261.70  
  Purchase #2 $250.91   4.462%   $262.1056   $262.11   $262.10   $262.10  
  Purchase #3 $61.38   3.761%   $63.6885   $63.69   $63.70   $63.70  
  Purchase #4 $235.71   13.573%   $267.7029   $267.70   $267.70   $267.70  
  Purchase #5 $129.78   7.521%   $139.5408   $139.54   $139.55   $139.50  
  Purchase #6 $132.56   11.794%   $148.1941   $148.19   $148.20   $148.20  
  Purchase #7 $136.48   13.500%   $154.9048   $154.90   $154.90   $154.90  
  7 purchase totals = $1,179.30       $1,297.8325   $1,297.83   $1,297.85   $1,297.80