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 $24.82   8.485%   $26.926   $26.93   $26.95   $26.90  
  Purchase #2 $174.68   3.567%   $180.9108   $180.91   $180.90   $180.90  
  Purchase #3 $205.62   6.271%   $218.5144   $218.51   $218.50   $218.50  
  Purchase #4 $10.81   7.404%   $11.6104   $11.61   $11.60   $11.60  
  Purchase #5 $130.43   6.525%   $138.9406   $138.94   $138.95   $138.90  
  Purchase #6 $114.43   11.656%   $127.768   $127.77   $127.75   $127.80  
  Purchase #7 $32.29   8.618%   $35.0728   $35.07   $35.05   $35.10  
  7 purchase totals = $693.08       $739.7430   $739.74   $739.70   $739.70