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 $111.34   13.847%   $126.7572   $126.76   $126.75   $126.80  
  Purchase #2 $222.49   11.675%   $248.4657   $248.47   $248.45   $248.50  
  Purchase #3 $49.92   10.563%   $55.193   $55.19   $55.20   $55.20  
  Purchase #4 $26.83   3.275%   $27.7087   $27.71   $27.70   $27.70  
  Purchase #5 $131.26   6.602%   $139.9258   $139.93   $139.95   $139.90  
  Purchase #6 $107.35   11.116%   $119.283   $119.28   $119.30   $119.30  
  Purchase #7 $199.52   3.459%   $206.4214   $206.42   $206.40   $206.40  
  7 purchase totals = $848.71       $923.7548   $923.76   $923.75   $923.80