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 $91.46   10.678%   $101.2261   $101.23   $101.25   $101.20  
  Purchase #2 $41.71   4.554%   $43.6095   $43.61   $43.60   $43.60  
  Purchase #3 $58.38   3.379%   $60.3527   $60.35   $60.35   $60.40  
  Purchase #4 $76.76   6.358%   $81.6404   $81.64   $81.65   $81.60  
  Purchase #5 $208.50   8.152%   $225.4969   $225.50   $225.50   $225.50  
  Purchase #6 $183.64   5.309%   $193.3894   $193.39   $193.40   $193.40  
  Purchase #7 $68.76   13.246%   $77.8679   $77.87   $77.85   $77.90  
  7 purchase totals = $729.21       $783.5829   $783.59   $783.60   $783.60