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 $208.82   8.283%   $226.1166   $226.12   $226.10   $226.10  
  Purchase #2 $102.79   6.298%   $109.2637   $109.26   $109.25   $109.30  
  Purchase #3 $100.46   5.743%   $106.2294   $106.23   $106.25   $106.20  
  Purchase #4 $166.68   7.629%   $179.396   $179.40   $179.40   $179.40  
  Purchase #5 $138.69   11.571%   $154.7378   $154.74   $154.75   $154.70  
  Purchase #6 $78.59   8.346%   $85.1491   $85.15   $85.15   $85.10  
  Purchase #7 $60.42   8.849%   $65.7666   $65.77   $65.75   $65.80  
  7 purchase totals = $856.45       $926.6592   $926.67   $926.65   $926.60