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 $191.87   8.536%   $208.248   $208.25   $208.25   $208.20  
  Purchase #2 $136.80   4.442%   $142.8767   $142.88   $142.90   $142.90  
  Purchase #3 $57.28   12.289%   $64.3191   $64.32   $64.30   $64.30  
  Purchase #4 $93.76   3.153%   $96.7163   $96.72   $96.70   $96.70  
  Purchase #5 $249.32   6.812%   $266.3037   $266.30   $266.30   $266.30  
  Purchase #6 $24.64   6.593%   $26.2645   $26.26   $26.25   $26.30  
  Purchase #7 $178.53   5.462%   $188.2813   $188.28   $188.30   $188.30  
  7 purchase totals = $932.20       $993.0096   $993.01   $993.00   $993.00