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 $67.62   11.827%   $75.6174   $75.62   $75.60   $75.60  
  Purchase #2 $69.79   12.521%   $78.5284   $78.53   $78.55   $78.50  
  Purchase #3 $86.33   8.461%   $93.6344   $93.63   $93.65   $93.60  
  Purchase #4 $163.83   12.108%   $183.6665   $183.67   $183.65   $183.70  
  Purchase #5 $237.73   11.684%   $265.5064   $265.51   $265.50   $265.50  
  Purchase #6 $53.54   3.643%   $55.4905   $55.49   $55.50   $55.50  
  Purchase #7 $137.69   5.443%   $145.1845   $145.18   $145.20   $145.20  
  7 purchase totals = $816.53       $897.6281   $897.63   $897.65   $897.60