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 $201.92   6.233%   $214.5057   $214.51   $214.50   $214.50  
  Purchase #2 $243.64   7.623%   $262.2127   $262.21   $262.20   $262.20  
  Purchase #3 $70.83   7.642%   $76.2428   $76.24   $76.25   $76.20  
  Purchase #4 $50.91   3.512%   $52.698   $52.70   $52.70   $52.70  
  Purchase #5 $149.90   4.727%   $156.9858   $156.99   $157.00   $157.00  
  Purchase #6 $62.67   8.548%   $68.027   $68.03   $68.05   $68.00  
  Purchase #7 $124.50   9.490%   $136.3151   $136.32   $136.30   $136.30  
  7 purchase totals = $904.37       $966.9871   $967.00   $967.00   $966.90