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 $234.69   11.124%   $260.7969   $260.80   $260.80   $260.80  
  Purchase #2 $125.57   13.757%   $142.8447   $142.84   $142.85   $142.80  
  Purchase #3 $126.26   10.858%   $139.9693   $139.97   $139.95   $140.00  
  Purchase #4 $101.42   13.670%   $115.2841   $115.28   $115.30   $115.30  
  Purchase #5 $108.48   5.572%   $114.5245   $114.52   $114.50   $114.50  
  Purchase #6 $142.76   6.543%   $152.1008   $152.10   $152.10   $152.10  
  Purchase #7 $58.26   5.526%   $61.4794   $61.48   $61.50   $61.50  
  7 purchase totals = $897.44       $986.9997   $986.99   $987.00   $987.00