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 $55.86   4.273%   $58.2469   $58.25   $58.25   $58.20  
  Purchase #2 $117.83   3.835%   $122.3488   $122.35   $122.35   $122.30  
  Purchase #3 $57.38   13.428%   $65.085   $65.09   $65.10   $65.10  
  Purchase #4 $240.66   6.142%   $255.4413   $255.44   $255.45   $255.40  
  Purchase #5 $191.27   8.761%   $208.0272   $208.03   $208.05   $208.00  
  Purchase #6 $170.84   5.506%   $180.2465   $180.25   $180.25   $180.20  
  Purchase #7 $43.57   12.208%   $48.889   $48.89   $48.90   $48.90  
  7 purchase totals = $877.41       $938.2847   $938.30   $938.35   $938.10