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 $158.30   6.255%   $168.2017   $168.20   $168.20   $168.20  
  Purchase #2 $160.90   3.137%   $165.9474   $165.95   $165.95   $165.90  
  Purchase #3 $105.87   7.816%   $114.1448   $114.14   $114.15   $114.10  
  Purchase #4 $211.66   6.484%   $225.384   $225.38   $225.40   $225.40  
  Purchase #5 $176.87   3.286%   $182.6819   $182.68   $182.70   $182.70  
  Purchase #6 $225.37   6.483%   $239.9807   $239.98   $240.00   $240.00  
  Purchase #7 $249.33   13.139%   $282.0895   $282.09   $282.10   $282.10  
  7 purchase totals = $1,288.30       $1,378.4300   $1,378.42   $1,378.50   $1,378.40