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 $248.73   5.197%   $261.6565   $261.66   $261.65   $261.70  
  Purchase #2 $118.71   6.532%   $126.4641   $126.46   $126.45   $126.50  
  Purchase #3 $65.26   6.448%   $69.468   $69.47   $69.45   $69.50  
  Purchase #4 $59.83   12.745%   $67.4553   $67.46   $67.45   $67.50  
  Purchase #5 $167.36   5.801%   $177.0686   $177.07   $177.05   $177.10  
  Purchase #6 $26.71   12.149%   $29.955   $29.96   $29.95   $30.00  
  Purchase #7 $41.32   4.364%   $43.1232   $43.12   $43.10   $43.10  
  7 purchase totals = $727.92       $775.1907   $775.20   $775.10   $775.40