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 $171.92   12.772%   $193.8776   $193.88   $193.90   $193.90  
  Purchase #2 $43.45   10.835%   $48.1578   $48.16   $48.15   $48.20  
  Purchase #3 $233.89   11.843%   $261.5896   $261.59   $261.60   $261.60  
  Purchase #4 $60.38   3.537%   $62.5156   $62.52   $62.50   $62.50  
  Purchase #5 $168.69   8.501%   $183.0303   $183.03   $183.05   $183.00  
  Purchase #6 $18.83   6.592%   $20.0713   $20.07   $20.05   $20.10  
  Purchase #7 $236.93   11.509%   $264.1983   $264.20   $264.20   $264.20  
  7 purchase totals = $934.09       $1,033.4405   $1,033.45   $1,033.45   $1,033.50