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 $236.65   6.567%   $252.1908   $252.19   $252.20   $252.20  
  Purchase #2 $212.47   7.747%   $228.9301   $228.93   $228.95   $228.90  
  Purchase #3 $208.41   4.563%   $217.9197   $217.92   $217.90   $217.90  
  Purchase #4 $210.85   12.208%   $236.5906   $236.59   $236.60   $236.60  
  Purchase #5 $72.44   11.752%   $80.9531   $80.95   $80.95   $81.00  
  Purchase #6 $158.43   11.440%   $176.5544   $176.55   $176.55   $176.60  
  Purchase #7 $196.30   3.252%   $202.6837   $202.68   $202.70   $202.70  
  7 purchase totals = $1,295.55       $1,395.8224   $1,395.81   $1,395.85   $1,395.90