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 $55.79   6.652%   $59.5012   $59.50   $59.50   $59.50  
  Purchase #2 $28.82   6.623%   $30.7287   $30.73   $30.75   $30.70  
  Purchase #3 $113.59   11.249%   $126.3677   $126.37   $126.35   $126.40  
  Purchase #4 $145.94   5.196%   $153.523   $153.52   $153.50   $153.50  
  Purchase #5 $143.83   11.812%   $160.8192   $160.82   $160.80   $160.80  
  Purchase #6 $171.35   10.130%   $188.7078   $188.71   $188.70   $188.70  
  Purchase #7 $23.25   5.114%   $24.439   $24.44   $24.45   $24.40  
  7 purchase totals = $682.57       $744.0866   $744.09   $744.05   $744.00