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 $75.46   9.432%   $82.5774   $82.58   $82.60   $82.60  
  Purchase #2 $240.66   10.592%   $266.1507   $266.15   $266.15   $266.20  
  Purchase #3 $12.90   5.229%   $13.5745   $13.57   $13.55   $13.60  
  Purchase #4 $130.32   5.403%   $137.3612   $137.36   $137.35   $137.40  
  Purchase #5 $61.95   9.659%   $67.9338   $67.93   $67.95   $67.90  
  Purchase #6 $25.75   5.772%   $27.2363   $27.24   $27.25   $27.20  
  Purchase #7 $85.54   13.601%   $97.1743   $97.17   $97.15   $97.20  
  7 purchase totals = $632.58       $692.0082   $692.00   $692.00   $692.10