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 $24.43   8.843%   $26.5903   $26.59   $26.60   $26.60  
  Purchase #2 $35.55   12.722%   $40.0727   $40.07   $40.05   $40.10  
  Purchase #3 $195.37   3.632%   $202.4658   $202.47   $202.45   $202.50  
  Purchase #4 $59.84   9.621%   $65.5972   $65.60   $65.60   $65.60  
  Purchase #5 $233.95   5.804%   $247.5285   $247.53   $247.55   $247.50  
  Purchase #6 $44.25   4.414%   $46.2032   $46.20   $46.20   $46.20  
  Purchase #7 $12.38   13.396%   $14.0384   $14.04   $14.05   $14.00  
  7 purchase totals = $605.77       $642.4961   $642.50   $642.50   $642.50