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 $9.72   12.105%   $10.8966   $10.90   $10.90   $10.90  
  Purchase #2 $51.47   11.546%   $57.4127   $57.41   $57.40   $57.40  
  Purchase #3 $190.48   8.234%   $206.1641   $206.16   $206.15   $206.20  
  Purchase #4 $196.62   8.834%   $213.9894   $213.99   $214.00   $214.00  
  Purchase #5 $153.33   3.569%   $158.8023   $158.80   $158.80   $158.80  
  Purchase #6 $172.26   11.116%   $191.4084   $191.41   $191.40   $191.40  
  Purchase #7 $155.83   9.775%   $171.0624   $171.06   $171.05   $171.10  
  7 purchase totals = $929.71       $1,009.7359   $1,009.73   $1,009.70   $1,009.80