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 $208.81   8.257%   $226.0514   $226.05   $226.05   $226.10  
  Purchase #2 $26.83   8.355%   $29.0716   $29.07   $29.05   $29.10  
  Purchase #3 $61.34   8.781%   $66.7263   $66.73   $66.75   $66.70  
  Purchase #4 $248.93   8.275%   $269.529   $269.53   $269.55   $269.50  
  Purchase #5 $72.49   13.317%   $82.1435   $82.14   $82.15   $82.10  
  Purchase #6 $106.46   11.526%   $118.7306   $118.73   $118.75   $118.70  
  Purchase #7 $70.56   8.144%   $76.3064   $76.31   $76.30   $76.30  
  7 purchase totals = $795.42       $868.5588   $868.56   $868.60   $868.50