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 $214.47   10.154%   $236.2473   $236.25   $236.25   $236.20  
  Purchase #2 $177.57   8.713%   $193.0417   $193.04   $193.05   $193.00  
  Purchase #3 $208.63   4.339%   $217.6825   $217.68   $217.70   $217.70  
  Purchase #4 $46.99   12.457%   $52.8435   $52.84   $52.85   $52.80  
  Purchase #5 $162.89   12.665%   $183.52   $183.52   $183.50   $183.50  
  Purchase #6 $245.81   5.683%   $259.7794   $259.78   $259.80   $259.80  
  Purchase #7 $239.44   4.716%   $250.732   $250.73   $250.75   $250.70  
  7 purchase totals = $1,295.80       $1,393.8464   $1,393.84   $1,393.90   $1,393.70