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 $202.65   6.107%   $215.0258   $215.03   $215.05   $215.00  
  Purchase #2 $81.54   5.646%   $86.1437   $86.14   $86.15   $86.10  
  Purchase #3 $250.44   13.781%   $284.9531   $284.95   $284.95   $285.00  
  Purchase #4 $132.62   8.788%   $144.2746   $144.27   $144.25   $144.30  
  Purchase #5 $222.53   6.812%   $237.6887   $237.69   $237.70   $237.70  
  Purchase #6 $226.39   5.557%   $238.9705   $238.97   $238.95   $239.00  
  Purchase #7 $249.77   4.181%   $260.2129   $260.21   $260.20   $260.20  
  7 purchase totals = $1,365.94       $1,467.2693   $1,467.26   $1,467.25   $1,467.30