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 $245.41   6.523%   $261.4181   $261.42   $261.40   $261.40  
  Purchase #2 $124.68   5.557%   $131.6085   $131.61   $131.60   $131.60  
  Purchase #3 $15.55   5.852%   $16.46   $16.46   $16.45   $16.50  
  Purchase #4 $22.84   6.198%   $24.2556   $24.26   $24.25   $24.30  
  Purchase #5 $245.69   3.514%   $254.3235   $254.32   $254.30   $254.30  
  Purchase #6 $92.46   13.384%   $104.8348   $104.83   $104.85   $104.80  
  Purchase #7 $219.86   5.409%   $231.7522   $231.75   $231.75   $231.80  
  7 purchase totals = $966.49       $1,024.6527   $1,024.65   $1,024.60   $1,024.70