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 $125.85   8.247%   $136.2288   $136.23   $136.25   $136.20  
  Purchase #2 $190.50   3.191%   $196.5789   $196.58   $196.60   $196.60  
  Purchase #3 $115.44   9.626%   $126.5523   $126.55   $126.55   $126.60  
  Purchase #4 $43.30   11.413%   $48.2418   $48.24   $48.25   $48.20  
  Purchase #5 $76.85   12.394%   $86.3748   $86.37   $86.35   $86.40  
  Purchase #6 $32.58   3.214%   $33.6271   $33.63   $33.65   $33.60  
  Purchase #7 $231.81   13.755%   $263.6955   $263.70   $263.70   $263.70  
  7 purchase totals = $816.33       $891.2992   $891.30   $891.35   $891.30