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 $180.39   9.232%   $197.0436   $197.04   $197.05   $197.00  
  Purchase #2 $175.67   10.174%   $193.5427   $193.54   $193.55   $193.50  
  Purchase #3 $54.76   3.260%   $56.5452   $56.55   $56.55   $56.50  
  Purchase #4 $246.41   4.357%   $257.1461   $257.15   $257.15   $257.10  
  Purchase #5 $197.27   9.423%   $215.8588   $215.86   $215.85   $215.90  
  Purchase #6 $30.80   11.125%   $34.2265   $34.23   $34.25   $34.20  
  Purchase #7 $51.64   8.501%   $56.0299   $56.03   $56.05   $56.00  
  7 purchase totals = $936.94       $1,010.3928   $1,010.40   $1,010.45   $1,010.20