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 $74.41   11.422%   $82.9091   $82.91   $82.90   $82.90  
  Purchase #2 $214.54   7.283%   $230.1649   $230.16   $230.15   $230.20  
  Purchase #3 $193.46   7.741%   $208.4357   $208.44   $208.45   $208.40  
  Purchase #4 $166.34   6.133%   $176.5416   $176.54   $176.55   $176.50  
  Purchase #5 $162.59   9.719%   $178.3921   $178.39   $178.40   $178.40  
  Purchase #6 $118.49   4.570%   $123.905   $123.91   $123.90   $123.90  
  Purchase #7 $240.41   3.562%   $248.9734   $248.97   $248.95   $249.00  
  7 purchase totals = $1,170.24       $1,249.3218   $1,249.32   $1,249.30   $1,249.30