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 $206.71   12.221%   $231.972   $231.97   $231.95   $232.00  
  Purchase #2 $9.27   9.335%   $10.1354   $10.14   $10.15   $10.10  
  Purchase #3 $55.78   11.756%   $62.3375   $62.34   $62.35   $62.30  
  Purchase #4 $237.87   9.832%   $261.2574   $261.26   $261.25   $261.30  
  Purchase #5 $139.54   13.642%   $158.576   $158.58   $158.60   $158.60  
  Purchase #6 $50.58   5.796%   $53.5116   $53.51   $53.50   $53.50  
  Purchase #7 $246.54   7.563%   $265.1858   $265.19   $265.20   $265.20  
  7 purchase totals = $946.29       $1,042.9757   $1,042.99   $1,043.00   $1,043.00