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 $240.62   13.854%   $273.9555   $273.96   $273.95   $274.00  
  Purchase #2 $224.70   12.474%   $252.7291   $252.73   $252.75   $252.70  
  Purchase #3 $163.41   8.162%   $176.7475   $176.75   $176.75   $176.70  
  Purchase #4 $91.75   4.835%   $96.1861   $96.19   $96.20   $96.20  
  Purchase #5 $140.32   9.716%   $153.9535   $153.95   $153.95   $154.00  
  Purchase #6 $195.48   5.434%   $206.1024   $206.10   $206.10   $206.10  
  Purchase #7 $210.59   8.493%   $228.4754   $228.48   $228.50   $228.50  
  7 purchase totals = $1,266.87       $1,388.1495   $1,388.16   $1,388.20   $1,388.20