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 $59.29   10.703%   $65.6358   $65.64   $65.65   $65.60  
  Purchase #2 $23.81   3.724%   $24.6967   $24.70   $24.70   $24.70  
  Purchase #3 $92.89   3.102%   $95.7714   $95.77   $95.75   $95.80  
  Purchase #4 $17.65   6.272%   $18.757   $18.76   $18.75   $18.80  
  Purchase #5 $188.28   5.665%   $198.9461   $198.95   $198.95   $198.90  
  Purchase #6 $152.84   8.538%   $165.8895   $165.89   $165.90   $165.90  
  Purchase #7 $59.68   9.833%   $65.5483   $65.55   $65.55   $65.50  
  7 purchase totals = $594.44       $635.2448   $635.26   $635.25   $635.20