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 $57.66   13.159%   $65.2475   $65.25   $65.25   $65.20  
  Purchase #2 $63.70   12.172%   $71.4536   $71.45   $71.45   $71.50  
  Purchase #3 $8.77   13.451%   $9.9497   $9.95   $9.95   $9.90  
  Purchase #4 $68.93   9.626%   $75.5652   $75.57   $75.55   $75.60  
  Purchase #5 $154.52   6.176%   $164.0632   $164.06   $164.05   $164.10  
  Purchase #6 $236.65   4.134%   $246.4331   $246.43   $246.45   $246.40  
  Purchase #7 $20.99   8.381%   $22.7492   $22.75   $22.75   $22.70  
  7 purchase totals = $611.22       $655.4615   $655.46   $655.45   $655.40