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 $118.77   4.681%   $124.3296   $124.33   $124.35   $124.30  
  Purchase #2 $107.97   5.843%   $114.2787   $114.28   $114.30   $114.30  
  Purchase #3 $59.68   13.458%   $67.7117   $67.71   $67.70   $67.70  
  Purchase #4 $163.95   11.535%   $182.8616   $182.86   $182.85   $182.90  
  Purchase #5 $239.63   5.486%   $252.7761   $252.78   $252.80   $252.80  
  Purchase #6 $182.60   4.400%   $190.6344   $190.63   $190.65   $190.60  
  Purchase #7 $53.93   10.275%   $59.4713   $59.47   $59.45   $59.50  
  7 purchase totals = $926.53       $992.0634   $992.06   $992.10   $992.10