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 $23.57   12.340%   $26.4785   $26.48   $26.50   $26.50  
  Purchase #2 $166.95   11.788%   $186.6301   $186.63   $186.65   $186.60  
  Purchase #3 $250.62   12.242%   $281.3009   $281.30   $281.30   $281.30  
  Purchase #4 $42.94   10.407%   $47.4088   $47.41   $47.40   $47.40  
  Purchase #5 $5.42   13.708%   $6.163   $6.16   $6.15   $6.20  
  Purchase #6 $171.43   13.267%   $194.1736   $194.17   $194.15   $194.20  
  Purchase #7 $142.33   10.543%   $157.3359   $157.34   $157.35   $157.30  
  7 purchase totals = $803.26       $899.4908   $899.49   $899.50   $899.50