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 $84.35   13.271%   $95.5441   $95.54   $95.55   $95.50  
  Purchase #2 $165.96   10.522%   $183.4223   $183.42   $183.40   $183.40  
  Purchase #3 $166.37   7.154%   $178.2721   $178.27   $178.25   $178.30  
  Purchase #4 $96.98   6.187%   $102.9802   $102.98   $103.00   $103.00  
  Purchase #5 $238.66   9.660%   $261.7146   $261.71   $261.70   $261.70  
  Purchase #6 $57.65   10.338%   $63.6099   $63.61   $63.60   $63.60  
  Purchase #7 $221.98   3.632%   $230.0423   $230.04   $230.05   $230.00  
  7 purchase totals = $1,031.95       $1,115.5855   $1,115.57   $1,115.55   $1,115.50