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 $119.65   6.671%   $127.6319   $127.63   $127.65   $127.60  
  Purchase #2 $6.32   4.509%   $6.605   $6.61   $6.60   $6.60  
  Purchase #3 $93.45   4.722%   $97.8627   $97.86   $97.85   $97.90  
  Purchase #4 $162.67   12.246%   $182.5906   $182.59   $182.60   $182.60  
  Purchase #5 $162.25   8.115%   $175.4166   $175.42   $175.40   $175.40  
  Purchase #6 $98.45   5.292%   $103.66   $103.66   $103.65   $103.70  
  Purchase #7 $156.92   3.123%   $161.8206   $161.82   $161.80   $161.80  
  7 purchase totals = $799.71       $855.5874   $855.59   $855.55   $855.60