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 $183.86   4.187%   $191.5582   $191.56   $191.55   $191.60  
  Purchase #2 $59.45   3.156%   $61.3262   $61.33   $61.35   $61.30  
  Purchase #3 $246.88   5.779%   $261.1472   $261.15   $261.15   $261.10  
  Purchase #4 $186.69   10.545%   $206.3765   $206.38   $206.40   $206.40  
  Purchase #5 $19.90   12.514%   $22.3903   $22.39   $22.40   $22.40  
  Purchase #6 $119.82   8.643%   $130.176   $130.18   $130.20   $130.20  
  Purchase #7 $145.53   12.256%   $163.3662   $163.37   $163.35   $163.40  
  7 purchase totals = $962.13       $1,036.3406   $1,036.36   $1,036.40   $1,036.40