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 $98.45   4.802%   $103.1776   $103.18   $103.20   $103.20  
  Purchase #2 $26.77   13.750%   $30.4509   $30.45   $30.45   $30.50  
  Purchase #3 $61.42   7.523%   $66.0406   $66.04   $66.05   $66.00  
  Purchase #4 $230.43   7.717%   $248.2123   $248.21   $248.20   $248.20  
  Purchase #5 $239.93   6.210%   $254.8297   $254.83   $254.85   $254.80  
  Purchase #6 $54.45   6.170%   $57.8096   $57.81   $57.80   $57.80  
  Purchase #7 $175.31   4.306%   $182.8588   $182.86   $182.85   $182.90  
  7 purchase totals = $886.76       $943.3795   $943.38   $943.40   $943.40