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 $32.90   6.207%   $34.9421   $34.94   $34.95   $34.90  
  Purchase #2 $137.39   13.754%   $156.2866   $156.29   $156.30   $156.30  
  Purchase #3 $234.62   5.772%   $248.1623   $248.16   $248.15   $248.20  
  Purchase #4 $114.36   8.366%   $123.9274   $123.93   $123.95   $123.90  
  Purchase #5 $116.48   11.448%   $129.8146   $129.81   $129.80   $129.80  
  Purchase #6 $123.86   12.678%   $139.563   $139.56   $139.55   $139.60  
  Purchase #7 $127.46   11.643%   $142.3002   $142.30   $142.30   $142.30  
  7 purchase totals = $887.07       $974.9962   $974.99   $975.00   $975.00