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 $131.69   3.708%   $136.5731   $136.57   $136.55   $136.60  
  Purchase #2 $85.92   10.455%   $94.9029   $94.90   $94.90   $94.90  
  Purchase #3 $150.89   6.204%   $160.2512   $160.25   $160.25   $160.30  
  Purchase #4 $22.39   5.372%   $23.5928   $23.59   $23.60   $23.60  
  Purchase #5 $241.73   3.693%   $250.6571   $250.66   $250.65   $250.70  
  Purchase #6 $231.71   12.438%   $260.5301   $260.53   $260.55   $260.50  
  Purchase #7 $161.74   8.291%   $175.1499   $175.15   $175.15   $175.10  
  7 purchase totals = $1,026.07       $1,101.6571   $1,101.65   $1,101.65   $1,101.70