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 $212.74   4.664%   $222.6622   $222.66   $222.65   $222.70  
  Purchase #2 $238.85   10.709%   $264.4284   $264.43   $264.45   $264.40  
  Purchase #3 $104.71   10.319%   $115.515   $115.52   $115.50   $115.50  
  Purchase #4 $190.84   13.435%   $216.4794   $216.48   $216.50   $216.50  
  Purchase #5 $125.39   5.233%   $131.9517   $131.95   $131.95   $132.00  
  Purchase #6 $237.57   8.284%   $257.2503   $257.25   $257.25   $257.30  
  Purchase #7 $57.88   4.248%   $60.3387   $60.34   $60.35   $60.30  
  7 purchase totals = $1,167.98       $1,268.6257   $1,268.63   $1,268.65   $1,268.70