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 $46.95   8.514%   $50.9473   $50.95   $50.95   $50.90  
  Purchase #2 $74.85   5.159%   $78.7115   $78.71   $78.70   $78.70  
  Purchase #3 $228.25   6.110%   $242.1961   $242.20   $242.20   $242.20  
  Purchase #4 $217.83   7.511%   $234.1912   $234.19   $234.20   $234.20  
  Purchase #5 $225.51   10.861%   $250.0026   $250.00   $250.00   $250.00  
  Purchase #6 $154.30   10.611%   $170.6728   $170.67   $170.65   $170.70  
  Purchase #7 $125.96   6.387%   $134.0051   $134.01   $134.00   $134.00  
  7 purchase totals = $1,073.65       $1,160.7266   $1,160.73   $1,160.70   $1,160.70