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 $231.98   13.197%   $262.5944   $262.59   $262.60   $262.60  
  Purchase #2 $117.35   8.622%   $127.4679   $127.47   $127.45   $127.50  
  Purchase #3 $85.27   12.356%   $95.806   $95.81   $95.80   $95.80  
  Purchase #4 $23.52   9.118%   $25.6646   $25.66   $25.65   $25.70  
  Purchase #5 $92.25   6.231%   $97.9981   $98.00   $98.00   $98.00  
  Purchase #6 $239.62   3.592%   $248.2272   $248.23   $248.25   $248.20  
  Purchase #7 $77.41   12.653%   $87.2047   $87.20   $87.20   $87.20  
  7 purchase totals = $867.40       $944.9629   $944.96   $944.95   $945.00