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 $92.59   3.672%   $95.9899   $95.99   $96.00   $96.00  
  Purchase #2 $160.81   9.754%   $176.4954   $176.50   $176.50   $176.50  
  Purchase #3 $228.36   13.615%   $259.4512   $259.45   $259.45   $259.50  
  Purchase #4 $149.36   3.271%   $154.2456   $154.25   $154.25   $154.20  
  Purchase #5 $73.75   13.339%   $83.5875   $83.59   $83.60   $83.60  
  Purchase #6 $17.75   10.779%   $19.6633   $19.66   $19.65   $19.70  
  Purchase #7 $22.88   8.515%   $24.8282   $24.83   $24.85   $24.80  
  7 purchase totals = $745.50       $814.2611   $814.27   $814.30   $814.30