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 $47.77   12.327%   $53.6586   $53.66   $53.65   $53.70  
  Purchase #2 $205.66   5.827%   $217.6438   $217.64   $217.65   $217.60  
  Purchase #3 $67.57   12.212%   $75.8216   $75.82   $75.80   $75.80  
  Purchase #4 $179.27   12.512%   $201.7003   $201.70   $201.70   $201.70  
  Purchase #5 $78.71   3.364%   $81.3578   $81.36   $81.35   $81.40  
  Purchase #6 $199.81   8.639%   $217.0716   $217.07   $217.05   $217.10  
  Purchase #7 $163.88   7.239%   $175.7433   $175.74   $175.75   $175.70  
  7 purchase totals = $942.67       $1,022.9970   $1,022.99   $1,022.95   $1,023.00