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 $248.70   5.563%   $262.5352   $262.54   $262.55   $262.50  
  Purchase #2 $158.55   8.248%   $171.6272   $171.63   $171.65   $171.60  
  Purchase #3 $156.95   9.561%   $171.956   $171.96   $171.95   $172.00  
  Purchase #4 $59.51   6.138%   $63.1627   $63.16   $63.15   $63.20  
  Purchase #5 $16.94   12.483%   $19.0546   $19.05   $19.05   $19.10  
  Purchase #6 $115.85   12.414%   $130.2316   $130.23   $130.25   $130.20  
  Purchase #7 $126.93   12.246%   $142.4738   $142.47   $142.45   $142.50  
  7 purchase totals = $883.43       $961.0411   $961.04   $961.05   $961.10