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 $201.73   12.344%   $226.6316   $226.63   $226.65   $226.60  
  Purchase #2 $25.51   7.565%   $27.4398   $27.44   $27.45   $27.40  
  Purchase #3 $196.43   5.745%   $207.7149   $207.71   $207.70   $207.70  
  Purchase #4 $110.80   13.872%   $126.1702   $126.17   $126.15   $126.20  
  Purchase #5 $89.54   12.849%   $101.045   $101.05   $101.05   $101.00  
  Purchase #6 $125.81   6.870%   $134.4531   $134.45   $134.45   $134.50  
  Purchase #7 $247.73   4.238%   $258.2288   $258.23   $258.25   $258.20  
  7 purchase totals = $997.55       $1,081.6834   $1,081.68   $1,081.70   $1,081.60