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 $55.37   11.548%   $61.7641   $61.76   $61.75   $61.80  
  Purchase #2 $77.56   5.699%   $81.9801   $81.98   $82.00   $82.00  
  Purchase #3 $108.78   7.501%   $116.9396   $116.94   $116.95   $116.90  
  Purchase #4 $218.28   9.563%   $239.1541   $239.15   $239.15   $239.20  
  Purchase #5 $78.91   8.625%   $85.716   $85.72   $85.70   $85.70  
  Purchase #6 $159.54   3.424%   $165.0026   $165.00   $165.00   $165.00  
  Purchase #7 $86.81   6.271%   $92.2539   $92.25   $92.25   $92.30  
  7 purchase totals = $785.25       $842.8104   $842.80   $842.80   $842.90