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 $223.95   10.860%   $248.271   $248.27   $248.25   $248.30  
  Purchase #2 $182.83   4.445%   $190.9568   $190.96   $190.95   $191.00  
  Purchase #3 $70.65   13.300%   $80.0465   $80.05   $80.05   $80.00  
  Purchase #4 $111.26   12.413%   $125.0707   $125.07   $125.05   $125.10  
  Purchase #5 $183.60   13.418%   $208.2354   $208.24   $208.25   $208.20  
  Purchase #6 $61.44   4.777%   $64.375   $64.38   $64.40   $64.40  
  Purchase #7 $34.43   10.433%   $38.0221   $38.02   $38.00   $38.00  
  7 purchase totals = $868.16       $954.9775   $954.99   $954.95   $955.00