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 $230.94   11.261%   $256.9462   $256.95   $256.95   $256.90  
  Purchase #2 $36.96   13.305%   $41.8775   $41.88   $41.90   $41.90  
  Purchase #3 $242.32   9.531%   $265.4155   $265.42   $265.40   $265.40  
  Purchase #4 $127.78   5.720%   $135.089   $135.09   $135.10   $135.10  
  Purchase #5 $42.48   10.669%   $47.0122   $47.01   $47.00   $47.00  
  Purchase #6 $70.28   4.194%   $73.2275   $73.23   $73.25   $73.20  
  Purchase #7 $166.49   12.309%   $186.9833   $186.98   $187.00   $187.00  
  7 purchase totals = $917.25       $1,006.5512   $1,006.56   $1,006.60   $1,006.50