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 $202.87   5.654%   $214.3403   $214.34   $214.35   $214.30  
  Purchase #2 $88.46   11.564%   $98.6895   $98.69   $98.70   $98.70  
  Purchase #3 $65.86   5.819%   $69.6924   $69.69   $69.70   $69.70  
  Purchase #4 $114.82   9.280%   $125.4753   $125.48   $125.50   $125.50  
  Purchase #5 $40.46   10.198%   $44.5861   $44.59   $44.60   $44.60  
  Purchase #6 $48.74   11.664%   $54.425   $54.43   $54.45   $54.40  
  Purchase #7 $166.34   3.243%   $171.7344   $171.73   $171.75   $171.70  
  7 purchase totals = $727.55       $778.9430   $778.95   $779.05   $778.90