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 $246.84   11.239%   $274.5823   $274.58   $274.60   $274.60  
  Purchase #2 $186.88   4.873%   $195.9867   $195.99   $196.00   $196.00  
  Purchase #3 $51.31   4.103%   $53.4152   $53.42   $53.40   $53.40  
  Purchase #4 $180.47   5.871%   $191.0654   $191.07   $191.05   $191.10  
  Purchase #5 $101.76   10.311%   $112.2525   $112.25   $112.25   $112.30  
  Purchase #6 $83.74   11.723%   $93.5568   $93.56   $93.55   $93.60  
  Purchase #7 $36.66   13.712%   $41.6868   $41.69   $41.70   $41.70  
  7 purchase totals = $887.66       $962.5457   $962.56   $962.55   $962.70