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 $64.66   3.247%   $66.7595   $66.76   $66.75   $66.80  
  Purchase #2 $22.77   4.509%   $23.7967   $23.80   $23.80   $23.80  
  Purchase #3 $209.54   6.754%   $223.6923   $223.69   $223.70   $223.70  
  Purchase #4 $54.77   10.451%   $60.494   $60.49   $60.50   $60.50  
  Purchase #5 $130.74   9.865%   $143.6375   $143.64   $143.65   $143.60  
  Purchase #6 $208.50   9.615%   $228.5473   $228.55   $228.55   $228.50  
  Purchase #7 $105.48   12.484%   $118.6481   $118.65   $118.65   $118.60  
  7 purchase totals = $796.46       $865.5754   $865.58   $865.60   $865.50