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 $246.97   5.661%   $260.951   $260.95   $260.95   $261.00  
  Purchase #2 $152.95   5.262%   $160.9982   $161.00   $161.00   $161.00  
  Purchase #3 $235.38   6.520%   $250.7268   $250.73   $250.75   $250.70  
  Purchase #4 $12.97   13.342%   $14.7005   $14.70   $14.70   $14.70  
  Purchase #5 $48.91   3.400%   $50.5729   $50.57   $50.55   $50.60  
  Purchase #6 $140.55   8.288%   $152.1988   $152.20   $152.20   $152.20  
  Purchase #7 $122.38   11.177%   $136.0584   $136.06   $136.05   $136.10  
  7 purchase totals = $960.11       $1,026.2066   $1,026.21   $1,026.20   $1,026.30