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 $12.95   8.236%   $14.0166   $14.02   $14.00   $14.00  
  Purchase #2 $98.36   3.792%   $102.0898   $102.09   $102.10   $102.10  
  Purchase #3 $228.89   7.643%   $246.3841   $246.38   $246.40   $246.40  
  Purchase #4 $131.92   7.404%   $141.6874   $141.69   $141.70   $141.70  
  Purchase #5 $26.93   4.573%   $28.1615   $28.16   $28.15   $28.20  
  Purchase #6 $138.80   13.722%   $157.8461   $157.85   $157.85   $157.80  
  Purchase #7 $35.79   4.602%   $37.4371   $37.44   $37.45   $37.40  
  7 purchase totals = $673.64       $727.6226   $727.63   $727.65   $727.60