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 $222.76   13.570%   $252.9885   $252.99   $253.00   $253.00  
  Purchase #2 $153.27   4.643%   $160.3863   $160.39   $160.40   $160.40  
  Purchase #3 $221.77   8.787%   $241.2569   $241.26   $241.25   $241.30  
  Purchase #4 $185.97   8.535%   $201.8425   $201.84   $201.85   $201.80  
  Purchase #5 $191.83   8.446%   $208.032   $208.03   $208.05   $208.00  
  Purchase #6 $162.75   12.425%   $182.9717   $182.97   $182.95   $183.00  
  Purchase #7 $85.33   9.339%   $93.299   $93.30   $93.30   $93.30  
  7 purchase totals = $1,223.68       $1,340.7769   $1,340.78   $1,340.80   $1,340.80