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 $184.41   5.153%   $193.9126   $193.91   $193.90   $193.90  
  Purchase #2 $216.76   3.589%   $224.5395   $224.54   $224.55   $224.50  
  Purchase #3 $208.45   3.628%   $216.0126   $216.01   $216.00   $216.00  
  Purchase #4 $57.54   9.263%   $62.8699   $62.87   $62.85   $62.90  
  Purchase #5 $76.42   13.734%   $86.9155   $86.92   $86.90   $86.90  
  Purchase #6 $226.44   11.584%   $252.6708   $252.67   $252.65   $252.70  
  Purchase #7 $135.57   8.659%   $147.309   $147.31   $147.30   $147.30  
  7 purchase totals = $1,105.59       $1,184.2299   $1,184.23   $1,184.15   $1,184.20