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 $52.25   8.527%   $56.7054   $56.71   $56.70   $56.70  
  Purchase #2 $153.99   3.268%   $159.0224   $159.02   $159.00   $159.00  
  Purchase #3 $172.72   12.762%   $194.7625   $194.76   $194.75   $194.80  
  Purchase #4 $158.71   3.685%   $164.5585   $164.56   $164.55   $164.60  
  Purchase #5 $37.34   7.376%   $40.0942   $40.09   $40.10   $40.10  
  Purchase #6 $20.99   3.177%   $21.6569   $21.66   $21.65   $21.70  
  Purchase #7 $227.25   5.277%   $239.242   $239.24   $239.25   $239.20  
  7 purchase totals = $823.25       $876.0419   $876.04   $876.00   $876.10