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 $147.96   11.696%   $165.2654   $165.27   $165.25   $165.30  
  Purchase #2 $160.42   13.849%   $182.6366   $182.64   $182.65   $182.60  
  Purchase #3 $15.68   12.238%   $17.5989   $17.60   $17.60   $17.60  
  Purchase #4 $203.40   9.159%   $222.0294   $222.03   $222.05   $222.00  
  Purchase #5 $43.60   8.746%   $47.4133   $47.41   $47.40   $47.40  
  Purchase #6 $130.61   13.598%   $148.3703   $148.37   $148.35   $148.40  
  Purchase #7 $227.43   9.444%   $248.9085   $248.91   $248.90   $248.90  
  7 purchase totals = $929.10       $1,032.2224   $1,032.23   $1,032.20   $1,032.20