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 $225.92   9.798%   $248.0556   $248.06   $248.05   $248.10  
  Purchase #2 $114.73   8.540%   $124.5279   $124.53   $124.55   $124.50  
  Purchase #3 $84.83   6.712%   $90.5238   $90.52   $90.50   $90.50  
  Purchase #4 $26.94   11.674%   $30.085   $30.09   $30.10   $30.10  
  Purchase #5 $248.52   11.395%   $276.8389   $276.84   $276.85   $276.80  
  Purchase #6 $185.80   4.391%   $193.9585   $193.96   $193.95   $194.00  
  Purchase #7 $240.43   9.487%   $263.2396   $263.24   $263.25   $263.20  
  7 purchase totals = $1,127.17       $1,227.2293   $1,227.24   $1,227.25   $1,227.20