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 $23.98   3.168%   $24.7397   $24.74   $24.75   $24.70  
  Purchase #2 $144.45   7.258%   $154.9342   $154.93   $154.95   $154.90  
  Purchase #3 $5.89   11.383%   $6.5605   $6.56   $6.55   $6.60  
  Purchase #4 $209.55   12.259%   $235.2387   $235.24   $235.25   $235.20  
  Purchase #5 $58.89   5.597%   $62.1861   $62.19   $62.20   $62.20  
  Purchase #6 $171.58   12.647%   $193.2797   $193.28   $193.30   $193.30  
  Purchase #7 $246.86   4.696%   $258.4525   $258.45   $258.45   $258.50  
  7 purchase totals = $861.20       $935.3914   $935.39   $935.45   $935.40