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 $246.36   6.177%   $261.5777   $261.58   $261.60   $261.60  
  Purchase #2 $139.27   5.873%   $147.4493   $147.45   $147.45   $147.40  
  Purchase #3 $219.62   5.748%   $232.2438   $232.24   $232.25   $232.20  
  Purchase #4 $59.94   6.724%   $63.9704   $63.97   $63.95   $64.00  
  Purchase #5 $185.47   12.660%   $208.9505   $208.95   $208.95   $209.00  
  Purchase #6 $102.38   3.550%   $106.0145   $106.01   $106.00   $106.00  
  Purchase #7 $215.71   3.194%   $222.5998   $222.60   $222.60   $222.60  
  7 purchase totals = $1,168.75       $1,242.8060   $1,242.80   $1,242.80   $1,242.80