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 $246.54   6.433%   $262.3999   $262.40   $262.40   $262.40  
  Purchase #2 $52.81   8.733%   $57.4219   $57.42   $57.40   $57.40  
  Purchase #3 $137.68   4.332%   $143.6443   $143.64   $143.65   $143.60  
  Purchase #4 $65.53   12.730%   $73.872   $73.87   $73.85   $73.90  
  Purchase #5 $23.77   3.496%   $24.601   $24.60   $24.60   $24.60  
  Purchase #6 $230.70   8.144%   $249.4882   $249.49   $249.50   $249.50  
  Purchase #7 $185.59   5.176%   $195.1961   $195.20   $195.20   $195.20  
  7 purchase totals = $942.62       $1,006.6234   $1,006.62   $1,006.60   $1,006.60