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 $52.38   13.143%   $59.2643   $59.26   $59.25   $59.30  
  Purchase #2 $77.44   12.399%   $87.0418   $87.04   $87.05   $87.00  
  Purchase #3 $95.62   7.808%   $103.086   $103.09   $103.10   $103.10  
  Purchase #4 $224.73   4.349%   $234.5035   $234.50   $234.50   $234.50  
  Purchase #5 $89.77   13.525%   $101.9114   $101.91   $101.90   $101.90  
  Purchase #6 $130.62   13.785%   $148.626   $148.63   $148.65   $148.60  
  Purchase #7 $84.76   3.327%   $87.58   $87.58   $87.60   $87.60  
  7 purchase totals = $755.32       $822.0130   $822.01   $822.05   $822.00