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 $58.30   3.445%   $60.3084   $60.31   $60.30   $60.30  
  Purchase #2 $208.38   8.423%   $225.9318   $225.93   $225.95   $225.90  
  Purchase #3 $83.68   6.624%   $89.223   $89.22   $89.20   $89.20  
  Purchase #4 $111.45   6.674%   $118.8882   $118.89   $118.90   $118.90  
  Purchase #5 $192.49   7.382%   $206.6996   $206.70   $206.70   $206.70  
  Purchase #6 $39.69   9.189%   $43.3371   $43.34   $43.35   $43.30  
  Purchase #7 $107.99   5.458%   $113.8841   $113.88   $113.90   $113.90  
  7 purchase totals = $801.98       $858.2722   $858.27   $858.30   $858.20