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 $186.83   11.663%   $208.62   $208.62   $208.60   $208.60  
  Purchase #2 $164.77   10.539%   $182.1351   $182.14   $182.15   $182.10  
  Purchase #3 $74.79   9.634%   $81.9953   $82.00   $82.00   $82.00  
  Purchase #4 $67.94   11.243%   $75.5785   $75.58   $75.60   $75.60  
  Purchase #5 $208.43   3.411%   $215.5395   $215.54   $215.55   $215.50  
  Purchase #6 $60.28   7.538%   $64.8239   $64.82   $64.80   $64.80  
  Purchase #7 $93.60   8.249%   $101.3211   $101.32   $101.30   $101.30  
  7 purchase totals = $856.64       $930.0134   $930.02   $930.00   $929.90