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 $58.61   8.523%   $63.6053   $63.61   $63.60   $63.60  
  Purchase #2 $5.65   13.391%   $6.4066   $6.41   $6.40   $6.40  
  Purchase #3 $163.70   3.705%   $169.7651   $169.77   $169.75   $169.80  
  Purchase #4 $219.96   13.684%   $250.0593   $250.06   $250.05   $250.10  
  Purchase #5 $71.42   11.143%   $79.3783   $79.38   $79.40   $79.40  
  Purchase #6 $151.97   11.657%   $169.6851   $169.69   $169.70   $169.70  
  Purchase #7 $100.28   3.119%   $103.4077   $103.41   $103.40   $103.40  
  7 purchase totals = $771.59       $842.3074   $842.33   $842.30   $842.40