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 $76.81   8.749%   $83.5301   $83.53   $83.55   $83.50  
  Purchase #2 $239.92   4.537%   $250.8052   $250.81   $250.80   $250.80  
  Purchase #3 $162.57   3.775%   $168.707   $168.71   $168.70   $168.70  
  Purchase #4 $231.83   6.796%   $247.5852   $247.59   $247.60   $247.60  
  Purchase #5 $236.49   8.249%   $255.9981   $256.00   $256.00   $256.00  
  Purchase #6 $126.77   3.582%   $131.3109   $131.31   $131.30   $131.30  
  Purchase #7 $98.39   9.419%   $107.6574   $107.66   $107.65   $107.70  
  7 purchase totals = $1,172.78       $1,245.5939   $1,245.61   $1,245.60   $1,245.60