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 $229.44   7.641%   $246.9715   $246.97   $246.95   $247.00  
  Purchase #2 $100.36   4.626%   $105.0027   $105.00   $105.00   $105.00  
  Purchase #3 $34.53   11.588%   $38.5313   $38.53   $38.55   $38.50  
  Purchase #4 $166.65   9.391%   $182.3001   $182.30   $182.30   $182.30  
  Purchase #5 $92.43   5.594%   $97.6005   $97.60   $97.60   $97.60  
  Purchase #6 $223.61   11.242%   $248.7482   $248.75   $248.75   $248.70  
  Purchase #7 $122.66   3.197%   $126.5814   $126.58   $126.60   $126.60  
  7 purchase totals = $969.68       $1,045.7357   $1,045.73   $1,045.75   $1,045.70