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 $23.64   10.789%   $26.1905   $26.19   $26.20   $26.20  
  Purchase #2 $150.33   4.624%   $157.2813   $157.28   $157.30   $157.30  
  Purchase #3 $79.89   6.325%   $84.943   $84.94   $84.95   $84.90  
  Purchase #4 $231.75   9.137%   $252.925   $252.93   $252.95   $252.90  
  Purchase #5 $114.82   10.738%   $127.1494   $127.15   $127.15   $127.10  
  Purchase #6 $50.46   3.764%   $52.3593   $52.36   $52.35   $52.40  
  Purchase #7 $186.74   11.375%   $207.9817   $207.98   $208.00   $208.00  
  7 purchase totals = $837.63       $908.8302   $908.83   $908.90   $908.80