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 $211.45   13.364%   $239.7082   $239.71   $239.70   $239.70  
  Purchase #2 $163.98   4.371%   $171.1476   $171.15   $171.15   $171.10  
  Purchase #3 $148.49   7.365%   $159.4263   $159.43   $159.45   $159.40  
  Purchase #4 $76.61   5.198%   $80.5922   $80.59   $80.60   $80.60  
  Purchase #5 $195.53   13.178%   $221.2969   $221.30   $221.30   $221.30  
  Purchase #6 $90.51   4.852%   $94.9015   $94.90   $94.90   $94.90  
  Purchase #7 $207.58   13.216%   $235.0138   $235.01   $235.00   $235.00  
  7 purchase totals = $1,094.15       $1,202.0865   $1,202.09   $1,202.10   $1,202.00