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 $184.87   6.393%   $196.6887   $196.69   $196.70   $196.70  
  Purchase #2 $62.65   10.696%   $69.351   $69.35   $69.35   $69.40  
  Purchase #3 $28.33   7.872%   $30.5601   $30.56   $30.55   $30.60  
  Purchase #4 $217.66   10.520%   $240.5578   $240.56   $240.55   $240.60  
  Purchase #5 $75.77   3.710%   $78.5811   $78.58   $78.60   $78.60  
  Purchase #6 $123.90   8.828%   $134.8379   $134.84   $134.85   $134.80  
  Purchase #7 $42.78   12.202%   $48   $48.00   $48.00   $48.00  
  7 purchase totals = $735.96       $798.5766   $798.58   $798.60   $798.70