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 $114.67   8.737%   $124.6887   $124.69   $124.70   $124.70  
  Purchase #2 $183.58   13.845%   $208.9967   $209.00   $209.00   $209.00  
  Purchase #3 $102.97   4.411%   $107.512   $107.51   $107.50   $107.50  
  Purchase #4 $65.57   5.488%   $69.1685   $69.17   $69.15   $69.20  
  Purchase #5 $73.91   11.264%   $82.2352   $82.24   $82.25   $82.20  
  Purchase #6 $149.65   4.756%   $156.7674   $156.77   $156.75   $156.80  
  Purchase #7 $26.27   8.611%   $28.5321   $28.53   $28.55   $28.50  
  7 purchase totals = $716.62       $777.9006   $777.91   $777.90   $777.90