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 $225.85   6.702%   $240.9865   $240.99   $241.00   $241.00  
  Purchase #2 $164.88   5.498%   $173.9451   $173.95   $173.95   $173.90  
  Purchase #3 $137.43   11.716%   $153.5313   $153.53   $153.55   $153.50  
  Purchase #4 $222.62   9.636%   $244.0717   $244.07   $244.05   $244.10  
  Purchase #5 $225.26   10.202%   $248.241   $248.24   $248.25   $248.20  
  Purchase #6 $175.51   6.704%   $187.2762   $187.28   $187.30   $187.30  
  Purchase #7 $242.76   13.524%   $275.5909   $275.59   $275.60   $275.60  
  7 purchase totals = $1,394.31       $1,523.6427   $1,523.65   $1,523.70   $1,523.60