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 $59.49   11.288%   $66.2052   $66.21   $66.20   $66.20  
  Purchase #2 $223.61   6.423%   $237.9725   $237.97   $237.95   $238.00  
  Purchase #3 $170.78   5.242%   $179.7323   $179.73   $179.75   $179.70  
  Purchase #4 $79.82   8.320%   $86.461   $86.46   $86.45   $86.50  
  Purchase #5 $110.33   3.380%   $114.0592   $114.06   $114.05   $114.10  
  Purchase #6 $157.96   11.862%   $176.6972   $176.70   $176.70   $176.70  
  Purchase #7 $56.89   10.800%   $63.0341   $63.03   $63.05   $63.00  
  7 purchase totals = $858.88       $924.1615   $924.16   $924.15   $924.20