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 $54.57   3.657%   $56.5656   $56.57   $56.55   $56.60  
  Purchase #2 $125.92   13.632%   $143.0854   $143.09   $143.10   $143.10  
  Purchase #3 $161.39   6.577%   $172.0046   $172.00   $172.00   $172.00  
  Purchase #4 $248.50   5.365%   $261.832   $261.83   $261.85   $261.80  
  Purchase #5 $217.92   6.646%   $232.403   $232.40   $232.40   $232.40  
  Purchase #6 $93.39   12.463%   $105.0292   $105.03   $105.05   $105.00  
  Purchase #7 $119.71   7.711%   $128.9408   $128.94   $128.95   $128.90  
  7 purchase totals = $1,021.40       $1,099.8606   $1,099.86   $1,099.90   $1,099.80