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 $206.50   13.430%   $234.233   $234.23   $234.25   $234.20  
  Purchase #2 $22.38   5.458%   $23.6015   $23.60   $23.60   $23.60  
  Purchase #3 $11.45   4.202%   $11.9311   $11.93   $11.95   $11.90  
  Purchase #4 $99.60   7.530%   $107.0999   $107.10   $107.10   $107.10  
  Purchase #5 $56.83   13.659%   $64.5924   $64.59   $64.60   $64.60  
  Purchase #6 $236.68   9.427%   $258.9918   $258.99   $259.00   $259.00  
  Purchase #7 $234.29   5.609%   $247.4313   $247.43   $247.45   $247.40  
  7 purchase totals = $867.73       $947.8810   $947.87   $947.95   $947.80