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 $229.74   11.784%   $256.8126   $256.81   $256.80   $256.80  
  Purchase #2 $38.91   10.397%   $42.9555   $42.96   $42.95   $43.00  
  Purchase #3 $42.68   11.103%   $47.4188   $47.42   $47.40   $47.40  
  Purchase #4 $102.82   11.429%   $114.5713   $114.57   $114.55   $114.60  
  Purchase #5 $63.64   5.726%   $67.284   $67.28   $67.30   $67.30  
  Purchase #6 $124.55   10.567%   $137.7112   $137.71   $137.70   $137.70  
  Purchase #7 $224.61   5.153%   $236.1842   $236.18   $236.20   $236.20  
  7 purchase totals = $826.95       $902.9376   $902.93   $902.90   $903.00