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 $22.81   7.623%   $24.5488   $24.55   $24.55   $24.50  
  Purchase #2 $242.75   5.457%   $255.9969   $256.00   $256.00   $256.00  
  Purchase #3 $207.37   8.403%   $224.7953   $224.80   $224.80   $224.80  
  Purchase #4 $42.32   12.871%   $47.767   $47.77   $47.75   $47.80  
  Purchase #5 $185.91   11.434%   $207.1669   $207.17   $207.15   $207.20  
  Purchase #6 $98.62   11.202%   $109.6674   $109.67   $109.65   $109.70  
  Purchase #7 $174.53   11.860%   $195.2293   $195.23   $195.25   $195.20  
  7 purchase totals = $974.31       $1,065.1716   $1,065.19   $1,065.15   $1,065.20