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 $192.76   13.563%   $218.904   $218.90   $218.90   $218.90  
  Purchase #2 $178.59   3.665%   $185.1353   $185.14   $185.15   $185.10  
  Purchase #3 $236.34   13.509%   $268.2672   $268.27   $268.25   $268.30  
  Purchase #4 $155.55   8.413%   $168.6364   $168.64   $168.65   $168.60  
  Purchase #5 $141.64   9.758%   $155.4612   $155.46   $155.45   $155.50  
  Purchase #6 $12.98   9.755%   $14.2462   $14.25   $14.25   $14.20  
  Purchase #7 $237.77   6.397%   $252.9801   $252.98   $253.00   $253.00  
  7 purchase totals = $1,155.63       $1,263.6304   $1,263.64   $1,263.65   $1,263.60