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 $41.87   13.724%   $47.6162   $47.62   $47.60   $47.60  
  Purchase #2 $54.27   8.399%   $58.8281   $58.83   $58.85   $58.80  
  Purchase #3 $137.37   13.238%   $155.555   $155.56   $155.55   $155.60  
  Purchase #4 $208.32   7.455%   $223.8503   $223.85   $223.85   $223.90  
  Purchase #5 $192.70   11.287%   $214.45   $214.45   $214.45   $214.50  
  Purchase #6 $11.95   5.801%   $12.6432   $12.64   $12.65   $12.60  
  Purchase #7 $93.49   10.276%   $103.097   $103.10   $103.10   $103.10  
  7 purchase totals = $739.97       $816.0398   $816.05   $816.05   $816.10