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 $146.64   6.696%   $156.459   $156.46   $156.45   $156.50  
  Purchase #2 $27.27   4.136%   $28.3979   $28.40   $28.40   $28.40  
  Purchase #3 $242.90   6.607%   $258.9484   $258.95   $258.95   $258.90  
  Purchase #4 $55.69   8.342%   $60.3357   $60.34   $60.35   $60.30  
  Purchase #5 $143.36   10.263%   $158.073   $158.07   $158.05   $158.10  
  Purchase #6 $186.58   11.271%   $207.6094   $207.61   $207.60   $207.60  
  Purchase #7 $131.95   3.225%   $136.2054   $136.21   $136.20   $136.20  
  7 purchase totals = $934.39       $1,006.0288   $1,006.04   $1,006.00   $1,006.00