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 $171.26   11.724%   $191.3385   $191.34   $191.35   $191.30  
  Purchase #2 $213.74   13.409%   $242.4004   $242.40   $242.40   $242.40  
  Purchase #3 $246.28   6.590%   $262.5099   $262.51   $262.50   $262.50  
  Purchase #4 $158.47   11.501%   $176.6956   $176.70   $176.70   $176.70  
  Purchase #5 $226.63   4.304%   $236.3842   $236.38   $236.40   $236.40  
  Purchase #6 $150.74   8.859%   $164.0941   $164.09   $164.10   $164.10  
  Purchase #7 $26.92   11.416%   $29.9932   $29.99   $30.00   $30.00  
  7 purchase totals = $1,194.04       $1,303.4159   $1,303.41   $1,303.45   $1,303.40