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 $103.99   13.800%   $118.3406   $118.34   $118.35   $118.30  
  Purchase #2 $234.43   11.417%   $261.1949   $261.19   $261.20   $261.20  
  Purchase #3 $73.86   6.545%   $78.6941   $78.69   $78.70   $78.70  
  Purchase #4 $156.60   7.239%   $167.9363   $167.94   $167.95   $167.90  
  Purchase #5 $147.39   10.738%   $163.2167   $163.22   $163.20   $163.20  
  Purchase #6 $162.61   7.768%   $175.2415   $175.24   $175.25   $175.20  
  Purchase #7 $98.95   11.854%   $110.6795   $110.68   $110.70   $110.70  
  7 purchase totals = $977.83       $1,075.3036   $1,075.30   $1,075.35   $1,075.20