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 $214.48   11.585%   $239.3275   $239.33   $239.35   $239.30  
  Purchase #2 $11.61   12.574%   $13.0698   $13.07   $13.05   $13.10  
  Purchase #3 $136.91   8.341%   $148.3297   $148.33   $148.35   $148.30  
  Purchase #4 $209.98   4.198%   $218.795   $218.80   $218.80   $218.80  
  Purchase #5 $23.54   12.215%   $26.4154   $26.42   $26.40   $26.40  
  Purchase #6 $98.52   5.369%   $103.8095   $103.81   $103.80   $103.80  
  Purchase #7 $247.83   5.571%   $261.6366   $261.64   $261.65   $261.60  
  7 purchase totals = $942.87       $1,011.3835   $1,011.40   $1,011.40   $1,011.30