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   10.201%   $261.5951   $261.60   $261.60   $261.60  
  Purchase #2 $144.28   8.119%   $155.9941   $155.99   $156.00   $156.00  
  Purchase #3 $75.99   8.356%   $82.3397   $82.34   $82.35   $82.30  
  Purchase #4 $65.47   7.585%   $70.4359   $70.44   $70.45   $70.40  
  Purchase #5 $87.64   6.486%   $93.3243   $93.32   $93.30   $93.30  
  Purchase #6 $21.78   3.650%   $22.575   $22.58   $22.60   $22.60  
  Purchase #7 $232.77   5.705%   $246.0495   $246.05   $246.05   $246.00  
  7 purchase totals = $865.31       $932.3136   $932.32   $932.35   $932.20