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 $230.81   13.369%   $261.667   $261.67   $261.65   $261.70  
  Purchase #2 $44.88   6.284%   $47.7003   $47.70   $47.70   $47.70  
  Purchase #3 $74.40   11.152%   $82.6971   $82.70   $82.70   $82.70  
  Purchase #4 $192.34   7.418%   $206.6078   $206.61   $206.60   $206.60  
  Purchase #5 $240.89   9.783%   $264.4563   $264.46   $264.45   $264.50  
  Purchase #6 $167.30   4.374%   $174.6177   $174.62   $174.60   $174.60  
  Purchase #7 $127.82   4.781%   $133.9311   $133.93   $133.95   $133.90  
  7 purchase totals = $1,078.44       $1,171.6773   $1,171.69   $1,171.65   $1,171.70