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 $241.58   10.755%   $267.5619   $267.56   $267.55   $267.60  
  Purchase #2 $59.70   3.688%   $61.9017   $61.90   $61.90   $61.90  
  Purchase #3 $242.56   8.661%   $263.5681   $263.57   $263.55   $263.60  
  Purchase #4 $127.60   3.243%   $131.7381   $131.74   $131.75   $131.70  
  Purchase #5 $93.44   5.782%   $98.8427   $98.84   $98.85   $98.80  
  Purchase #6 $149.62   9.792%   $164.2708   $164.27   $164.25   $164.30  
  Purchase #7 $169.58   10.102%   $186.711   $186.71   $186.70   $186.70  
  7 purchase totals = $1,084.08       $1,174.5943   $1,174.59   $1,174.55   $1,174.60