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 $67.68   13.223%   $76.6293   $76.63   $76.65   $76.60  
  Purchase #2 $33.47   13.772%   $38.0795   $38.08   $38.10   $38.10  
  Purchase #3 $15.37   4.470%   $16.057   $16.06   $16.05   $16.10  
  Purchase #4 $204.95   3.787%   $212.7115   $212.71   $212.70   $212.70  
  Purchase #5 $108.81   4.304%   $113.4932   $113.49   $113.50   $113.50  
  Purchase #6 $67.69   12.130%   $75.9008   $75.90   $75.90   $75.90  
  Purchase #7 $210.99   11.488%   $235.2285   $235.23   $235.25   $235.20  
  7 purchase totals = $708.96       $768.0998   $768.10   $768.15   $768.10