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 $239.51   10.848%   $265.492   $265.49   $265.50   $265.50  
  Purchase #2 $34.66   5.197%   $36.4613   $36.46   $36.45   $36.50  
  Purchase #3 $203.42   9.427%   $222.5964   $222.60   $222.60   $222.60  
  Purchase #4 $163.85   7.738%   $176.5287   $176.53   $176.55   $176.50  
  Purchase #5 $187.65   12.267%   $210.669   $210.67   $210.65   $210.70  
  Purchase #6 $73.58   6.520%   $78.3774   $78.38   $78.40   $78.40  
  Purchase #7 $56.66   3.447%   $58.6131   $58.61   $58.60   $58.60  
  7 purchase totals = $959.33       $1,048.7379   $1,048.74   $1,048.75   $1,048.80