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 $59.84   8.490%   $64.9204   $64.92   $64.90   $64.90  
  Purchase #2 $250.82   5.576%   $264.8057   $264.81   $264.80   $264.80  
  Purchase #3 $66.78   3.394%   $69.0465   $69.05   $69.05   $69.00  
  Purchase #4 $146.80   8.105%   $158.6981   $158.70   $158.70   $158.70  
  Purchase #5 $225.25   6.267%   $239.3664   $239.37   $239.35   $239.40  
  Purchase #6 $43.71   7.667%   $47.0612   $47.06   $47.05   $47.10  
  Purchase #7 $168.39   10.245%   $185.6416   $185.64   $185.65   $185.60  
  7 purchase totals = $961.59       $1,029.5399   $1,029.55   $1,029.50   $1,029.50