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 $117.95   7.626%   $126.9449   $126.94   $126.95   $126.90  
  Purchase #2 $8.37   12.638%   $9.4278   $9.43   $9.45   $9.40  
  Purchase #3 $176.29   7.149%   $188.893   $188.89   $188.90   $188.90  
  Purchase #4 $86.77   13.376%   $98.3764   $98.38   $98.40   $98.40  
  Purchase #5 $109.86   11.562%   $122.562   $122.56   $122.55   $122.60  
  Purchase #6 $122.78   6.686%   $130.9891   $130.99   $131.00   $131.00  
  Purchase #7 $69.86   3.690%   $72.4378   $72.44   $72.45   $72.40  
  7 purchase totals = $691.88       $749.6310   $749.63   $749.70   $749.60