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 $57.49   4.774%   $60.2346   $60.23   $60.25   $60.20  
  Purchase #2 $237.95   8.806%   $258.9039   $258.90   $258.90   $258.90  
  Purchase #3 $181.30   13.827%   $206.3684   $206.37   $206.35   $206.40  
  Purchase #4 $90.26   8.735%   $98.1442   $98.14   $98.15   $98.10  
  Purchase #5 $230.85   7.639%   $248.4846   $248.48   $248.50   $248.50  
  Purchase #6 $76.91   6.286%   $81.7446   $81.74   $81.75   $81.70  
  Purchase #7 $48.25   11.575%   $53.8349   $53.83   $53.85   $53.80  
  7 purchase totals = $923.01       $1,007.7152   $1,007.69   $1,007.75   $1,007.60