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 $208.65   10.536%   $230.6334   $230.63   $230.65   $230.60  
  Purchase #2 $15.42   11.405%   $17.1787   $17.18   $17.20   $17.20  
  Purchase #3 $85.45   4.305%   $89.1286   $89.13   $89.15   $89.10  
  Purchase #4 $171.25   6.609%   $182.5679   $182.57   $182.55   $182.60  
  Purchase #5 $36.90   3.247%   $38.0981   $38.10   $38.10   $38.10  
  Purchase #6 $242.58   12.622%   $273.1984   $273.20   $273.20   $273.20  
  Purchase #7 $227.43   11.253%   $253.0227   $253.02   $253.00   $253.00  
  7 purchase totals = $987.68       $1,083.8278   $1,083.83   $1,083.85   $1,083.80