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 $208.27   9.466%   $227.9848   $227.98   $228.00   $228.00  
  Purchase #2 $34.91   3.162%   $36.0139   $36.01   $36.00   $36.00  
  Purchase #3 $38.86   3.600%   $40.259   $40.26   $40.25   $40.30  
  Purchase #4 $132.78   5.208%   $139.6952   $139.70   $139.70   $139.70  
  Purchase #5 $168.39   8.749%   $183.1224   $183.12   $183.10   $183.10  
  Purchase #6 $200.40   4.435%   $209.2877   $209.29   $209.30   $209.30  
  Purchase #7 $215.43   11.338%   $239.8555   $239.86   $239.85   $239.90  
  7 purchase totals = $999.04       $1,076.2185   $1,076.22   $1,076.20   $1,076.30