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 $89.91   9.489%   $98.4416   $98.44   $98.45   $98.40  
  Purchase #2 $241.81   8.304%   $261.8899   $261.89   $261.90   $261.90  
  Purchase #3 $191.25   4.330%   $199.5311   $199.53   $199.55   $199.50  
  Purchase #4 $189.37   12.129%   $212.3387   $212.34   $212.35   $212.30  
  Purchase #5 $50.97   11.395%   $56.778   $56.78   $56.80   $56.80  
  Purchase #6 $55.46   8.214%   $60.0155   $60.02   $60.00   $60.00  
  Purchase #7 $62.37   7.253%   $66.8937   $66.89   $66.90   $66.90  
  7 purchase totals = $881.14       $955.8885   $955.89   $955.95   $955.80