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 $206.47   5.627%   $218.0881   $218.09   $218.10   $218.10  
  Purchase #2 $79.53   3.778%   $82.5346   $82.53   $82.55   $82.50  
  Purchase #3 $44.85   5.321%   $47.2365   $47.24   $47.25   $47.20  
  Purchase #4 $67.69   13.411%   $76.7679   $76.77   $76.75   $76.80  
  Purchase #5 $135.47   6.247%   $143.9328   $143.93   $143.95   $143.90  
  Purchase #6 $216.46   11.849%   $242.1083   $242.11   $242.10   $242.10  
  Purchase #7 $186.40   8.668%   $202.5572   $202.56   $202.55   $202.60  
  7 purchase totals = $936.87       $1,013.2254   $1,013.23   $1,013.25   $1,013.20