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 $54.65   6.539%   $58.2236   $58.22   $58.20   $58.20  
  Purchase #2 $157.93   3.605%   $163.6234   $163.62   $163.60   $163.60  
  Purchase #3 $233.76   13.772%   $265.9534   $265.95   $265.95   $266.00  
  Purchase #4 $73.90   5.613%   $78.048   $78.05   $78.05   $78.00  
  Purchase #5 $31.73   6.246%   $33.7119   $33.71   $33.70   $33.70  
  Purchase #6 $158.77   10.654%   $175.6854   $175.69   $175.70   $175.70  
  Purchase #7 $109.40   12.713%   $123.308   $123.31   $123.30   $123.30  
  7 purchase totals = $820.14       $898.5537   $898.55   $898.50   $898.50