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 $234.44   11.396%   $261.1568   $261.16   $261.15   $261.20  
  Purchase #2 $218.55   13.385%   $247.8029   $247.80   $247.80   $247.80  
  Purchase #3 $117.92   7.260%   $126.481   $126.48   $126.50   $126.50  
  Purchase #4 $61.56   6.224%   $65.3915   $65.39   $65.40   $65.40  
  Purchase #5 $106.39   4.721%   $111.4127   $111.41   $111.40   $111.40  
  Purchase #6 $240.55   5.373%   $253.4748   $253.47   $253.45   $253.50  
  Purchase #7 $135.66   9.507%   $148.5572   $148.56   $148.55   $148.60  
  7 purchase totals = $1,115.07       $1,214.2769   $1,214.27   $1,214.25   $1,214.40