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 $198.38   13.556%   $225.2724   $225.27   $225.25   $225.30  
  Purchase #2 $195.96   9.336%   $214.2548   $214.25   $214.25   $214.30  
  Purchase #3 $219.75   8.202%   $237.7739   $237.77   $237.75   $237.80  
  Purchase #4 $55.63   3.167%   $57.3918   $57.39   $57.40   $57.40  
  Purchase #5 $247.85   10.818%   $274.6624   $274.66   $274.65   $274.70  
  Purchase #6 $55.44   5.600%   $58.5446   $58.54   $58.55   $58.50  
  Purchase #7 $149.53   10.140%   $164.6923   $164.69   $164.70   $164.70  
  7 purchase totals = $1,122.54       $1,232.5922   $1,232.57   $1,232.55   $1,232.70