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 $221.51   12.255%   $248.6561   $248.66   $248.65   $248.70  
  Purchase #2 $40.85   4.307%   $42.6094   $42.61   $42.60   $42.60  
  Purchase #3 $149.25   5.665%   $157.705   $157.71   $157.70   $157.70  
  Purchase #4 $171.95   11.697%   $192.063   $192.06   $192.05   $192.10  
  Purchase #5 $249.27   8.459%   $270.3557   $270.36   $270.35   $270.40  
  Purchase #6 $55.38   7.614%   $59.5966   $59.60   $59.60   $59.60  
  Purchase #7 $170.92   13.874%   $194.6334   $194.63   $194.65   $194.60  
  7 purchase totals = $1,059.13       $1,165.6192   $1,165.63   $1,165.60   $1,165.70