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 $101.38   9.799%   $111.3142   $111.31   $111.30   $111.30  
  Purchase #2 $24.38   8.546%   $26.4635   $26.46   $26.45   $26.50  
  Purchase #3 $207.63   4.615%   $217.2121   $217.21   $217.20   $217.20  
  Purchase #4 $64.83   4.863%   $67.9827   $67.98   $68.00   $68.00  
  Purchase #5 $128.73   4.626%   $134.685   $134.69   $134.70   $134.70  
  Purchase #6 $115.63   5.286%   $121.7422   $121.74   $121.75   $121.70  
  Purchase #7 $225.49   6.394%   $239.9078   $239.91   $239.90   $239.90  
  7 purchase totals = $868.07       $919.3075   $919.30   $919.30   $919.30