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 $55.36   12.253%   $62.1433   $62.14   $62.15   $62.10  
  Purchase #2 $49.32   6.602%   $52.5761   $52.58   $52.60   $52.60  
  Purchase #3 $99.89   9.609%   $109.4884   $109.49   $109.50   $109.50  
  Purchase #4 $38.36   10.474%   $42.3778   $42.38   $42.40   $42.40  
  Purchase #5 $210.50   4.341%   $219.6378   $219.64   $219.65   $219.60  
  Purchase #6 $177.54   9.217%   $193.9039   $193.90   $193.90   $193.90  
  Purchase #7 $57.69   9.298%   $63.054   $63.05   $63.05   $63.10  
  7 purchase totals = $688.66       $743.1813   $743.18   $743.25   $743.20