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 $237.38   11.737%   $265.2413   $265.24   $265.25   $265.20  
  Purchase #2 $187.38   3.324%   $193.6085   $193.61   $193.60   $193.60  
  Purchase #3 $194.51   10.610%   $215.1475   $215.15   $215.15   $215.10  
  Purchase #4 $214.45   9.863%   $235.6012   $235.60   $235.60   $235.60  
  Purchase #5 $180.40   5.829%   $190.9155   $190.92   $190.90   $190.90  
  Purchase #6 $56.52   11.353%   $62.9367   $62.94   $62.95   $62.90  
  Purchase #7 $208.94   5.441%   $220.3084   $220.31   $220.30   $220.30  
  7 purchase totals = $1,279.58       $1,383.7591   $1,383.77   $1,383.75   $1,383.60