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 $248.33   7.220%   $266.2594   $266.26   $266.25   $266.30  
  Purchase #2 $114.97   6.324%   $122.2407   $122.24   $122.25   $122.20  
  Purchase #3 $141.36   6.153%   $150.0579   $150.06   $150.05   $150.10  
  Purchase #4 $42.79   9.854%   $47.0065   $47.01   $47.00   $47.00  
  Purchase #5 $176.53   8.726%   $191.934   $191.93   $191.95   $191.90  
  Purchase #6 $178.84   3.690%   $185.4392   $185.44   $185.45   $185.40  
  Purchase #7 $196.90   3.624%   $204.0357   $204.04   $204.05   $204.00  
  7 purchase totals = $1,099.72       $1,166.9734   $1,166.98   $1,167.00   $1,166.90