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 $241.26   3.585%   $249.9092   $249.91   $249.90   $249.90  
  Purchase #2 $232.83   11.366%   $259.2935   $259.29   $259.30   $259.30  
  Purchase #3 $228.87   3.252%   $236.3129   $236.31   $236.30   $236.30  
  Purchase #4 $157.43   4.763%   $164.9284   $164.93   $164.95   $164.90  
  Purchase #5 $139.94   13.340%   $158.608   $158.61   $158.60   $158.60  
  Purchase #6 $46.47   5.357%   $48.9594   $48.96   $48.95   $49.00  
  Purchase #7 $116.76   13.239%   $132.2179   $132.22   $132.20   $132.20  
  7 purchase totals = $1,163.56       $1,250.2293   $1,250.23   $1,250.20   $1,250.20