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 $247.69   5.386%   $261.0306   $261.03   $261.05   $261.00  
  Purchase #2 $220.66   4.372%   $230.3073   $230.31   $230.30   $230.30  
  Purchase #3 $161.96   6.147%   $171.9157   $171.92   $171.90   $171.90  
  Purchase #4 $15.61   12.716%   $17.595   $17.60   $17.60   $17.60  
  Purchase #5 $170.98   3.790%   $177.4601   $177.46   $177.45   $177.50  
  Purchase #6 $135.77   5.293%   $142.9563   $142.96   $142.95   $143.00  
  Purchase #7 $185.50   11.392%   $206.6322   $206.63   $206.65   $206.60  
  7 purchase totals = $1,138.17       $1,207.8972   $1,207.91   $1,207.90   $1,207.90