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 $77.28   11.866%   $86.45   $86.45   $86.45   $86.50  
  Purchase #2 $159.74   12.831%   $180.2362   $180.24   $180.25   $180.20  
  Purchase #3 $106.42   7.757%   $114.675   $114.68   $114.70   $114.70  
  Purchase #4 $101.51   6.510%   $108.1183   $108.12   $108.10   $108.10  
  Purchase #5 $220.56   6.514%   $234.9273   $234.93   $234.95   $234.90  
  Purchase #6 $121.48   3.385%   $125.5921   $125.59   $125.60   $125.60  
  Purchase #7 $46.46   3.380%   $48.0303   $48.03   $48.05   $48.00  
  7 purchase totals = $833.45       $898.0292   $898.04   $898.10   $898.00