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 $234.81   13.539%   $266.6009   $266.60   $266.60   $266.60  
  Purchase #2 $62.55   10.529%   $69.1359   $69.14   $69.15   $69.10  
  Purchase #3 $206.64   7.420%   $221.9727   $221.97   $221.95   $222.00  
  Purchase #4 $233.99   12.189%   $262.511   $262.51   $262.50   $262.50  
  Purchase #5 $228.69   12.351%   $256.9355   $256.94   $256.95   $256.90  
  Purchase #6 $226.40   12.323%   $254.2993   $254.30   $254.30   $254.30  
  Purchase #7 $59.25   3.684%   $61.4328   $61.43   $61.45   $61.40  
  7 purchase totals = $1,252.33       $1,392.8881   $1,392.89   $1,392.90   $1,392.80