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 $54.63   12.680%   $61.5571   $61.56   $61.55   $61.60  
  Purchase #2 $99.93   7.690%   $107.6146   $107.61   $107.60   $107.60  
  Purchase #3 $49.80   8.662%   $54.1137   $54.11   $54.10   $54.10  
  Purchase #4 $74.27   7.154%   $79.5833   $79.58   $79.60   $79.60  
  Purchase #5 $232.70   12.188%   $261.0615   $261.06   $261.05   $261.10  
  Purchase #6 $205.88   4.859%   $215.8837   $215.88   $215.90   $215.90  
  Purchase #7 $41.90   11.717%   $46.8094   $46.81   $46.80   $46.80  
  7 purchase totals = $759.11       $826.6233   $826.61   $826.60   $826.70