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 $10.46   10.538%   $11.5623   $11.56   $11.55   $11.60  
  Purchase #2 $192.87   3.506%   $199.632   $199.63   $199.65   $199.60  
  Purchase #3 $119.53   6.464%   $127.2564   $127.26   $127.25   $127.30  
  Purchase #4 $154.25   5.683%   $163.016   $163.02   $163.00   $163.00  
  Purchase #5 $113.26   8.553%   $122.9471   $122.95   $122.95   $122.90  
  Purchase #6 $39.60   8.564%   $42.9913   $42.99   $43.00   $43.00  
  Purchase #7 $94.49   9.488%   $103.4552   $103.46   $103.45   $103.50  
  7 purchase totals = $724.46       $770.8603   $770.87   $770.85   $770.90