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 $163.75   13.559%   $185.9529   $185.95   $185.95   $186.00  
  Purchase #2 $198.49   8.869%   $216.0941   $216.09   $216.10   $216.10  
  Purchase #3 $8.51   13.688%   $9.6748   $9.67   $9.65   $9.70  
  Purchase #4 $28.79   5.363%   $30.334   $30.33   $30.35   $30.30  
  Purchase #5 $207.74   6.858%   $221.9868   $221.99   $222.00   $222.00  
  Purchase #6 $153.99   3.680%   $159.6568   $159.66   $159.65   $159.70  
  Purchase #7 $82.91   6.427%   $88.2386   $88.24   $88.25   $88.20  
  7 purchase totals = $844.18       $911.9380   $911.93   $911.95   $912.00