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 $81.80   13.871%   $93.1465   $93.15   $93.15   $93.10  
  Purchase #2 $62.81   12.141%   $70.4358   $70.44   $70.45   $70.40  
  Purchase #3 $42.67   8.247%   $46.189   $46.19   $46.20   $46.20  
  Purchase #4 $77.72   10.449%   $85.841   $85.84   $85.85   $85.80  
  Purchase #5 $57.63   12.657%   $64.9242   $64.92   $64.90   $64.90  
  Purchase #6 $114.80   4.325%   $119.7651   $119.77   $119.75   $119.80  
  Purchase #7 $239.52   9.498%   $262.2696   $262.27   $262.25   $262.30  
  7 purchase totals = $676.95       $742.5712   $742.58   $742.55   $742.50