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 $236.58   10.523%   $261.4753   $261.48   $261.50   $261.50  
  Purchase #2 $43.62   12.763%   $49.1872   $49.19   $49.20   $49.20  
  Purchase #3 $51.70   4.223%   $53.8833   $53.88   $53.90   $53.90  
  Purchase #4 $186.86   4.432%   $195.1416   $195.14   $195.15   $195.10  
  Purchase #5 $77.38   10.456%   $85.4709   $85.47   $85.45   $85.50  
  Purchase #6 $64.34   8.378%   $69.7304   $69.73   $69.75   $69.70  
  Purchase #7 $55.30   4.581%   $57.8333   $57.83   $57.85   $57.80  
  7 purchase totals = $715.78       $772.7220   $772.72   $772.80   $772.70