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 $30.89   11.498%   $34.4417   $34.44   $34.45   $34.40  
  Purchase #2 $115.77   10.583%   $128.0219   $128.02   $128.00   $128.00  
  Purchase #3 $11.50   11.655%   $12.8403   $12.84   $12.85   $12.80  
  Purchase #4 $27.67   9.514%   $30.3025   $30.30   $30.30   $30.30  
  Purchase #5 $54.98   3.136%   $56.7042   $56.70   $56.70   $56.70  
  Purchase #6 $243.55   7.329%   $261.3998   $261.40   $261.40   $261.40  
  Purchase #7 $224.71   12.287%   $252.3201   $252.32   $252.30   $252.30  
  7 purchase totals = $709.07       $776.0305   $776.02   $776.00   $775.90