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 $237.26   9.572%   $259.9705   $259.97   $259.95   $260.00  
  Purchase #2 $54.56   4.203%   $56.8532   $56.85   $56.85   $56.90  
  Purchase #3 $231.88   12.840%   $261.6534   $261.65   $261.65   $261.70  
  Purchase #4 $94.39   13.664%   $107.2874   $107.29   $107.30   $107.30  
  Purchase #5 $67.36   9.184%   $73.5463   $73.55   $73.55   $73.50  
  Purchase #6 $78.87   9.788%   $86.5898   $86.59   $86.60   $86.60  
  Purchase #7 $189.86   3.289%   $196.1045   $196.10   $196.10   $196.10  
  7 purchase totals = $954.18       $1,042.0051   $1,042.00   $1,042.00   $1,042.10