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 $67.77   7.246%   $72.6806   $72.68   $72.70   $72.70  
  Purchase #2 $29.62   9.104%   $32.3166   $32.32   $32.30   $32.30  
  Purchase #3 $144.81   7.652%   $155.8909   $155.89   $155.90   $155.90  
  Purchase #4 $196.76   5.446%   $207.4755   $207.48   $207.50   $207.50  
  Purchase #5 $20.89   12.688%   $23.5405   $23.54   $23.55   $23.50  
  Purchase #6 $186.46   3.728%   $193.4112   $193.41   $193.40   $193.40  
  Purchase #7 $238.42   13.233%   $269.9701   $269.97   $269.95   $270.00  
  7 purchase totals = $884.73       $955.2854   $955.29   $955.30   $955.30