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 $247.93   8.561%   $269.1553   $269.16   $269.15   $269.20  
  Purchase #2 $20.33   12.151%   $22.8003   $22.80   $22.80   $22.80  
  Purchase #3 $63.77   9.278%   $69.6866   $69.69   $69.70   $69.70  
  Purchase #4 $116.91   3.856%   $121.418   $121.42   $121.40   $121.40  
  Purchase #5 $109.60   8.357%   $118.7593   $118.76   $118.75   $118.80  
  Purchase #6 $175.44   3.186%   $181.0295   $181.03   $181.05   $181.00  
  Purchase #7 $215.25   8.264%   $233.0383   $233.04   $233.05   $233.00  
  7 purchase totals = $949.23       $1,015.8873   $1,015.90   $1,015.90   $1,015.90