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 $77.62   6.614%   $82.7538   $82.75   $82.75   $82.80  
  Purchase #2 $176.88   10.634%   $195.6894   $195.69   $195.70   $195.70  
  Purchase #3 $53.90   12.195%   $60.4731   $60.47   $60.45   $60.50  
  Purchase #4 $215.61   11.387%   $240.1615   $240.16   $240.15   $240.20  
  Purchase #5 $114.39   13.562%   $129.9036   $129.90   $129.90   $129.90  
  Purchase #6 $202.54   3.178%   $208.9767   $208.98   $209.00   $209.00  
  Purchase #7 $161.99   3.855%   $168.2347   $168.23   $168.25   $168.20  
  7 purchase totals = $1,002.93       $1,086.1928   $1,086.18   $1,086.20   $1,086.30