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 $114.70   12.422%   $128.948   $128.95   $128.95   $128.90  
  Purchase #2 $236.56   13.495%   $268.4838   $268.48   $268.50   $268.50  
  Purchase #3 $137.87   11.415%   $153.6079   $153.61   $153.60   $153.60  
  Purchase #4 $175.99   4.831%   $184.4921   $184.49   $184.50   $184.50  
  Purchase #5 $43.60   5.630%   $46.0547   $46.05   $46.05   $46.10  
  Purchase #6 $250.30   8.837%   $272.419   $272.42   $272.40   $272.40  
  Purchase #7 $68.28   12.806%   $77.0239   $77.02   $77.00   $77.00  
  7 purchase totals = $1,027.30       $1,131.0294   $1,131.02   $1,131.00   $1,131.00