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 $224.43   10.820%   $248.7133   $248.71   $248.70   $248.70  
  Purchase #2 $31.61   11.509%   $35.248   $35.25   $35.25   $35.20  
  Purchase #3 $103.38   10.646%   $114.3858   $114.39   $114.40   $114.40  
  Purchase #4 $199.49   5.658%   $210.7771   $210.78   $210.80   $210.80  
  Purchase #5 $216.46   8.750%   $235.4003   $235.40   $235.40   $235.40  
  Purchase #6 $129.29   11.135%   $143.6864   $143.69   $143.70   $143.70  
  Purchase #7 $163.72   9.387%   $179.0884   $179.09   $179.10   $179.10  
  7 purchase totals = $1,068.38       $1,167.2993   $1,167.31   $1,167.35   $1,167.30