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 $249.59   8.871%   $271.7311   $271.73   $271.75   $271.70  
  Purchase #2 $180.67   13.812%   $205.6241   $205.62   $205.60   $205.60  
  Purchase #3 $206.25   8.790%   $224.3794   $224.38   $224.40   $224.40  
  Purchase #4 $43.46   7.509%   $46.7234   $46.72   $46.70   $46.70  
  Purchase #5 $231.85   3.693%   $240.4122   $240.41   $240.40   $240.40  
  Purchase #6 $156.69   4.616%   $163.9228   $163.92   $163.90   $163.90  
  Purchase #7 $46.62   7.640%   $50.1818   $50.18   $50.20   $50.20  
  7 purchase totals = $1,115.13       $1,202.9748   $1,202.96   $1,202.95   $1,202.90