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 $68.69   11.526%   $76.6072   $76.61   $76.60   $76.60  
  Purchase #2 $13.27   12.421%   $14.9183   $14.92   $14.90   $14.90  
  Purchase #3 $162.55   7.338%   $174.4779   $174.48   $174.50   $174.50  
  Purchase #4 $180.58   10.437%   $199.4271   $199.43   $199.45   $199.40  
  Purchase #5 $10.94   13.859%   $12.4562   $12.46   $12.45   $12.50  
  Purchase #6 $236.84   5.502%   $249.8709   $249.87   $249.85   $249.90  
  Purchase #7 $244.69   7.185%   $262.271   $262.27   $262.25   $262.30  
  7 purchase totals = $917.56       $990.0286   $990.04   $990.00   $990.10