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 $182.59   8.448%   $198.0152   $198.02   $198.00   $198.00  
  Purchase #2 $45.84   8.194%   $49.5961   $49.60   $49.60   $49.60  
  Purchase #3 $102.89   8.688%   $111.8291   $111.83   $111.85   $111.80  
  Purchase #4 $220.30   5.350%   $232.0861   $232.09   $232.10   $232.10  
  Purchase #5 $230.80   13.665%   $262.3388   $262.34   $262.35   $262.30  
  Purchase #6 $115.80   3.141%   $119.4373   $119.44   $119.45   $119.40  
  Purchase #7 $78.71   5.342%   $82.9147   $82.91   $82.90   $82.90  
  7 purchase totals = $976.93       $1,056.2173   $1,056.23   $1,056.25   $1,056.10