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 $10.61   10.783%   $11.7541   $11.75   $11.75   $11.80  
  Purchase #2 $174.38   11.189%   $193.8914   $193.89   $193.90   $193.90  
  Purchase #3 $111.66   10.452%   $123.3307   $123.33   $123.35   $123.30  
  Purchase #4 $115.90   5.520%   $122.2977   $122.30   $122.30   $122.30  
  Purchase #5 $126.53   8.266%   $136.989   $136.99   $137.00   $137.00  
  Purchase #6 $162.65   10.441%   $179.6323   $179.63   $179.65   $179.60  
  Purchase #7 $145.60   7.175%   $156.0468   $156.05   $156.05   $156.00  
  7 purchase totals = $847.33       $923.9420   $923.94   $924.00   $923.90