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 $44.33   13.819%   $50.456   $50.46   $50.45   $50.50  
  Purchase #2 $203.86   10.201%   $224.6558   $224.66   $224.65   $224.70  
  Purchase #3 $76.54   3.491%   $79.212   $79.21   $79.20   $79.20  
  Purchase #4 $176.71   11.839%   $197.6307   $197.63   $197.65   $197.60  
  Purchase #5 $196.74   4.872%   $206.3252   $206.33   $206.35   $206.30  
  Purchase #6 $107.99   5.110%   $113.5083   $113.51   $113.50   $113.50  
  Purchase #7 $139.28   3.716%   $144.4556   $144.46   $144.45   $144.50  
  7 purchase totals = $945.45       $1,016.2436   $1,016.26   $1,016.25   $1,016.30