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 $240.61   12.528%   $270.7536   $270.75   $270.75   $270.80  
  Purchase #2 $149.40   9.759%   $163.9799   $163.98   $164.00   $164.00  
  Purchase #3 $51.63   3.345%   $53.357   $53.36   $53.35   $53.40  
  Purchase #4 $176.27   5.850%   $186.5818   $186.58   $186.60   $186.60  
  Purchase #5 $187.76   13.265%   $212.6664   $212.67   $212.65   $212.70  
  Purchase #6 $217.28   7.361%   $233.274   $233.27   $233.25   $233.30  
  Purchase #7 $232.34   3.681%   $240.8924   $240.89   $240.90   $240.90  
  7 purchase totals = $1,255.29       $1,361.5051   $1,361.50   $1,361.50   $1,361.70