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 $213.93   11.873%   $239.3299   $239.33   $239.35   $239.30  
  Purchase #2 $167.72   11.653%   $187.2644   $187.26   $187.25   $187.30  
  Purchase #3 $138.63   11.330%   $154.3368   $154.34   $154.35   $154.30  
  Purchase #4 $55.30   5.838%   $58.5284   $58.53   $58.55   $58.50  
  Purchase #5 $233.70   11.712%   $261.0709   $261.07   $261.05   $261.10  
  Purchase #6 $130.50   4.275%   $136.0789   $136.08   $136.10   $136.10  
  Purchase #7 $19.68   12.856%   $22.2101   $22.21   $22.20   $22.20  
  7 purchase totals = $959.46       $1,058.8194   $1,058.82   $1,058.85   $1,058.80