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 $237.73   13.272%   $269.2815   $269.28   $269.30   $269.30  
  Purchase #2 $224.94   4.798%   $235.7326   $235.73   $235.75   $235.70  
  Purchase #3 $149.32   9.794%   $163.9444   $163.94   $163.95   $163.90  
  Purchase #4 $195.74   6.807%   $209.064   $209.06   $209.05   $209.10  
  Purchase #5 $115.97   10.176%   $127.7711   $127.77   $127.75   $127.80  
  Purchase #6 $7.91   3.775%   $8.2086   $8.21   $8.20   $8.20  
  Purchase #7 $217.72   3.519%   $225.3816   $225.38   $225.40   $225.40  
  7 purchase totals = $1,149.33       $1,239.3838   $1,239.37   $1,239.40   $1,239.40