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 $175.54   10.501%   $193.9735   $193.97   $193.95   $194.00  
  Purchase #2 $50.76   9.730%   $55.6989   $55.70   $55.70   $55.70  
  Purchase #3 $173.53   8.490%   $188.2627   $188.26   $188.25   $188.30  
  Purchase #4 $231.60   11.847%   $259.0377   $259.04   $259.05   $259.00  
  Purchase #5 $81.55   6.522%   $86.8687   $86.87   $86.85   $86.90  
  Purchase #6 $207.37   9.274%   $226.6015   $226.60   $226.60   $226.60  
  Purchase #7 $221.42   12.780%   $249.7175   $249.72   $249.70   $249.70  
  7 purchase totals = $1,141.77       $1,260.1605   $1,260.16   $1,260.10   $1,260.20