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 $226.51   10.148%   $249.4962   $249.50   $249.50   $249.50  
  Purchase #2 $142.61   11.285%   $158.7035   $158.70   $158.70   $158.70  
  Purchase #3 $158.58   9.488%   $173.6261   $173.63   $173.65   $173.60  
  Purchase #4 $81.32   4.207%   $84.7411   $84.74   $84.75   $84.70  
  Purchase #5 $180.49   3.480%   $186.7711   $186.77   $186.75   $186.80  
  Purchase #6 $226.92   13.360%   $257.2365   $257.24   $257.25   $257.20  
  Purchase #7 $55.63   5.102%   $58.4682   $58.47   $58.45   $58.50  
  7 purchase totals = $1,072.06       $1,169.0427   $1,169.05   $1,169.05   $1,169.00