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 $56.53   6.610%   $60.2666   $60.27   $60.25   $60.30  
  Purchase #2 $103.90   10.196%   $114.4936   $114.49   $114.50   $114.50  
  Purchase #3 $217.94   9.681%   $239.0388   $239.04   $239.05   $239.00  
  Purchase #4 $245.96   3.605%   $254.8269   $254.83   $254.85   $254.80  
  Purchase #5 $248.55   5.274%   $261.6585   $261.66   $261.65   $261.70  
  Purchase #6 $200.77   13.186%   $227.2435   $227.24   $227.25   $227.20  
  Purchase #7 $151.72   10.610%   $167.8175   $167.82   $167.80   $167.80  
  7 purchase totals = $1,225.37       $1,325.3454   $1,325.35   $1,325.35   $1,325.30