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 $239.86   8.376%   $259.9507   $259.95   $259.95   $260.00  
  Purchase #2 $33.27   10.840%   $36.8765   $36.88   $36.90   $36.90  
  Purchase #3 $173.91   6.865%   $185.8489   $185.85   $185.85   $185.80  
  Purchase #4 $109.53   5.430%   $115.4775   $115.48   $115.50   $115.50  
  Purchase #5 $104.71   11.184%   $116.4208   $116.42   $116.40   $116.40  
  Purchase #6 $157.68   10.859%   $174.8025   $174.80   $174.80   $174.80  
  Purchase #7 $119.26   5.545%   $125.873   $125.87   $125.85   $125.90  
  7 purchase totals = $938.22       $1,015.2499   $1,015.25   $1,015.25   $1,015.30