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 $67.33   11.593%   $75.1356   $75.14   $75.15   $75.10  
  Purchase #2 $186.58   3.190%   $192.5319   $192.53   $192.55   $192.50  
  Purchase #3 $77.54   4.548%   $81.0665   $81.07   $81.05   $81.10  
  Purchase #4 $198.60   4.730%   $207.9938   $207.99   $208.00   $208.00  
  Purchase #5 $225.97   10.587%   $249.8934   $249.89   $249.90   $249.90  
  Purchase #6 $69.60   5.388%   $73.35   $73.35   $73.35   $73.40  
  Purchase #7 $207.36   13.517%   $235.3889   $235.39   $235.40   $235.40  
  7 purchase totals = $1,032.98       $1,115.3601   $1,115.36   $1,115.40   $1,115.40