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 $239.48   8.277%   $259.3018   $259.30   $259.30   $259.30  
  Purchase #2 $104.38   4.761%   $109.3495   $109.35   $109.35   $109.30  
  Purchase #3 $205.58   5.268%   $216.41   $216.41   $216.40   $216.40  
  Purchase #4 $10.36   8.496%   $11.2402   $11.24   $11.25   $11.20  
  Purchase #5 $186.43   3.445%   $192.8525   $192.85   $192.85   $192.90  
  Purchase #6 $57.67   4.739%   $60.403   $60.40   $60.40   $60.40  
  Purchase #7 $16.35   6.386%   $17.3941   $17.39   $17.40   $17.40  
  7 purchase totals = $820.25       $866.9511   $866.94   $866.95   $866.90