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 $39.50   13.308%   $44.7567   $44.76   $44.75   $44.80  
  Purchase #2 $122.57   5.758%   $129.6276   $129.63   $129.65   $129.60  
  Purchase #3 $198.60   3.823%   $206.1925   $206.19   $206.20   $206.20  
  Purchase #4 $49.40   7.605%   $53.1569   $53.16   $53.15   $53.20  
  Purchase #5 $192.48   8.470%   $208.7831   $208.78   $208.80   $208.80  
  Purchase #6 $112.62   13.296%   $127.594   $127.59   $127.60   $127.60  
  Purchase #7 $72.65   13.548%   $82.4926   $82.49   $82.50   $82.50  
  7 purchase totals = $787.82       $852.6034   $852.60   $852.65   $852.70