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 $53.55   9.396%   $58.5816   $58.58   $58.60   $58.60  
  Purchase #2 $238.36   4.856%   $249.9348   $249.93   $249.95   $249.90  
  Purchase #3 $197.76   13.110%   $223.6863   $223.69   $223.70   $223.70  
  Purchase #4 $228.40   7.509%   $245.5506   $245.55   $245.55   $245.60  
  Purchase #5 $54.64   8.455%   $59.2598   $59.26   $59.25   $59.30  
  Purchase #6 $239.93   10.815%   $265.8784   $265.88   $265.90   $265.90  
  Purchase #7 $94.58   9.755%   $103.8063   $103.81   $103.80   $103.80  
  7 purchase totals = $1,107.22       $1,206.6978   $1,206.70   $1,206.75   $1,206.80