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 $24.69   5.463%   $26.0388   $26.04   $26.05   $26.00  
  Purchase #2 $115.70   3.284%   $119.4996   $119.50   $119.50   $119.50  
  Purchase #3 $119.88   12.587%   $134.9693   $134.97   $134.95   $135.00  
  Purchase #4 $14.39   5.199%   $15.1381   $15.14   $15.15   $15.10  
  Purchase #5 $70.38   13.699%   $80.0214   $80.02   $80.00   $80.00  
  Purchase #6 $47.78   8.667%   $51.9211   $51.92   $51.90   $51.90  
  Purchase #7 $146.81   12.837%   $165.656   $165.66   $165.65   $165.70  
  7 purchase totals = $539.63       $593.2443   $593.25   $593.20   $593.20