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 $241.49   11.270%   $268.7059   $268.71   $268.70   $268.70  
  Purchase #2 $106.99   6.602%   $114.0535   $114.05   $114.05   $114.10  
  Purchase #3 $238.58   13.780%   $271.4563   $271.46   $271.45   $271.50  
  Purchase #4 $155.83   6.704%   $166.2768   $166.28   $166.30   $166.30  
  Purchase #5 $202.44   5.591%   $213.7584   $213.76   $213.75   $213.80  
  Purchase #6 $244.50   9.293%   $267.2214   $267.22   $267.20   $267.20  
  Purchase #7 $173.31   3.613%   $179.5717   $179.57   $179.55   $179.60  
  7 purchase totals = $1,363.14       $1,481.0440   $1,481.05   $1,481.00   $1,481.20