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 $89.44   9.550%   $97.9815   $97.98   $98.00   $98.00  
  Purchase #2 $73.81   13.380%   $83.6858   $83.69   $83.70   $83.70  
  Purchase #3 $248.32   5.522%   $262.0322   $262.03   $262.05   $262.00  
  Purchase #4 $147.62   4.578%   $154.378   $154.38   $154.40   $154.40  
  Purchase #5 $68.56   8.381%   $74.306   $74.31   $74.30   $74.30  
  Purchase #6 $101.76   6.313%   $108.1841   $108.18   $108.20   $108.20  
  Purchase #7 $154.70   6.702%   $165.068   $165.07   $165.05   $165.10  
  7 purchase totals = $884.21       $945.6356   $945.64   $945.70   $945.70