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 $162.78   3.718%   $168.8322   $168.83   $168.85   $168.80  
  Purchase #2 $180.96   11.653%   $202.0473   $202.05   $202.05   $202.00  
  Purchase #3 $198.84   4.589%   $207.9648   $207.96   $207.95   $208.00  
  Purchase #4 $86.41   5.421%   $91.0943   $91.09   $91.10   $91.10  
  Purchase #5 $200.59   6.650%   $213.9292   $213.93   $213.95   $213.90  
  Purchase #6 $53.92   4.611%   $56.4063   $56.41   $56.40   $56.40  
  Purchase #7 $213.99   3.257%   $220.9597   $220.96   $220.95   $221.00  
  7 purchase totals = $1,097.49       $1,161.2338   $1,161.23   $1,161.25   $1,161.20