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 $57.58   8.732%   $62.6079   $62.61   $62.60   $62.60  
  Purchase #2 $227.32   11.616%   $253.7255   $253.73   $253.75   $253.70  
  Purchase #3 $120.30   3.373%   $124.3577   $124.36   $124.35   $124.40  
  Purchase #4 $114.85   9.215%   $125.4334   $125.43   $125.45   $125.40  
  Purchase #5 $126.29   5.864%   $133.6956   $133.70   $133.70   $133.70  
  Purchase #6 $72.50   11.105%   $80.5511   $80.55   $80.55   $80.60  
  Purchase #7 $222.38   11.626%   $248.2339   $248.23   $248.25   $248.20  
  7 purchase totals = $941.22       $1,028.6051   $1,028.61   $1,028.65   $1,028.60