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 $21.72   11.383%   $24.1924   $24.19   $24.20   $24.20  
  Purchase #2 $238.74   5.533%   $251.9495   $251.95   $251.95   $251.90  
  Purchase #3 $113.44   5.274%   $119.4228   $119.42   $119.40   $119.40  
  Purchase #4 $67.36   9.811%   $73.9687   $73.97   $73.95   $74.00  
  Purchase #5 $188.96   8.744%   $205.4827   $205.48   $205.50   $205.50  
  Purchase #6 $214.28   6.382%   $227.9553   $227.96   $227.95   $228.00  
  Purchase #7 $154.72   6.308%   $164.4797   $164.48   $164.50   $164.50  
  7 purchase totals = $999.22       $1,067.4511   $1,067.45   $1,067.45   $1,067.50