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 $179.72   13.243%   $203.5203   $203.52   $203.50   $203.50  
  Purchase #2 $240.44   13.817%   $273.6616   $273.66   $273.65   $273.70  
  Purchase #3 $142.71   13.132%   $161.4507   $161.45   $161.45   $161.50  
  Purchase #4 $196.98   13.531%   $223.6334   $223.63   $223.65   $223.60  
  Purchase #5 $115.41   8.384%   $125.086   $125.09   $125.10   $125.10  
  Purchase #6 $242.32   7.668%   $260.9011   $260.90   $260.90   $260.90  
  Purchase #7 $59.49   11.758%   $66.4848   $66.48   $66.50   $66.50  
  7 purchase totals = $1,177.07       $1,314.7379   $1,314.73   $1,314.75   $1,314.80