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 $208.73   10.688%   $231.0391   $231.04   $231.05   $231.00  
  Purchase #2 $232.98   8.353%   $252.4408   $252.44   $252.45   $252.40  
  Purchase #3 $77.85   4.592%   $81.4249   $81.42   $81.40   $81.40  
  Purchase #4 $158.31   8.448%   $171.684   $171.68   $171.70   $171.70  
  Purchase #5 $219.55   12.489%   $246.9696   $246.97   $246.95   $247.00  
  Purchase #6 $65.78   7.509%   $70.7194   $70.72   $70.70   $70.70  
  Purchase #7 $38.44   12.795%   $43.3584   $43.36   $43.35   $43.40  
  7 purchase totals = $1,001.64       $1,097.6362   $1,097.63   $1,097.60   $1,097.60