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 $15.68   3.637%   $16.2503   $16.25   $16.25   $16.30  
  Purchase #2 $167.33   8.629%   $181.7689   $181.77   $181.75   $181.80  
  Purchase #3 $114.92   7.423%   $123.4505   $123.45   $123.45   $123.50  
  Purchase #4 $117.99   12.779%   $133.0679   $133.07   $133.05   $133.10  
  Purchase #5 $60.60   6.775%   $64.7057   $64.71   $64.70   $64.70  
  Purchase #6 $233.29   11.533%   $260.1953   $260.20   $260.20   $260.20  
  Purchase #7 $76.71   9.812%   $84.2368   $84.24   $84.25   $84.20  
  7 purchase totals = $786.52       $863.6754   $863.69   $863.65   $863.80