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 $235.73   10.687%   $260.9225   $260.92   $260.90   $260.90  
  Purchase #2 $58.93   3.338%   $60.8971   $60.90   $60.90   $60.90  
  Purchase #3 $96.90   8.845%   $105.4708   $105.47   $105.45   $105.50  
  Purchase #4 $230.61   13.863%   $262.5795   $262.58   $262.60   $262.60  
  Purchase #5 $11.87   13.288%   $13.4473   $13.45   $13.45   $13.40  
  Purchase #6 $199.85   10.702%   $221.2379   $221.24   $221.25   $221.20  
  Purchase #7 $57.90   10.692%   $64.0907   $64.09   $64.10   $64.10  
  7 purchase totals = $891.79       $988.6458   $988.65   $988.65   $988.60