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 $208.61   6.717%   $222.6223   $222.62   $222.60   $222.60  
  Purchase #2 $40.44   3.593%   $41.893   $41.89   $41.90   $41.90  
  Purchase #3 $163.27   8.242%   $176.7267   $176.73   $176.75   $176.70  
  Purchase #4 $123.70   4.352%   $129.0834   $129.08   $129.10   $129.10  
  Purchase #5 $111.56   13.676%   $126.8169   $126.82   $126.80   $126.80  
  Purchase #6 $23.29   9.246%   $25.4434   $25.44   $25.45   $25.40  
  Purchase #7 $49.63   5.865%   $52.5408   $52.54   $52.55   $52.50  
  7 purchase totals = $720.50       $775.1265   $775.12   $775.15   $775.00