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 $222.33   8.618%   $241.4904   $241.49   $241.50   $241.50  
  Purchase #2 $165.68   8.255%   $179.3569   $179.36   $179.35   $179.40  
  Purchase #3 $182.48   8.209%   $197.4598   $197.46   $197.45   $197.50  
  Purchase #4 $208.42   13.511%   $236.5796   $236.58   $236.60   $236.60  
  Purchase #5 $9.30   3.614%   $9.6361   $9.64   $9.65   $9.60  
  Purchase #6 $51.83   3.600%   $53.6959   $53.70   $53.70   $53.70  
  Purchase #7 $236.41   11.738%   $264.1598   $264.16   $264.15   $264.20  
  7 purchase totals = $1,076.45       $1,182.3785   $1,182.39   $1,182.40   $1,182.50