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 $239.95   8.788%   $261.0368   $261.04   $261.05   $261.00  
  Purchase #2 $165.44   11.563%   $184.5698   $184.57   $184.55   $184.60  
  Purchase #3 $127.26   11.502%   $141.8974   $141.90   $141.90   $141.90  
  Purchase #4 $90.61   4.262%   $94.4718   $94.47   $94.45   $94.50  
  Purchase #5 $168.61   8.236%   $182.4967   $182.50   $182.50   $182.50  
  Purchase #6 $34.94   3.125%   $36.0319   $36.03   $36.05   $36.00  
  Purchase #7 $108.57   6.322%   $115.4338   $115.43   $115.45   $115.40  
  7 purchase totals = $935.38       $1,015.9382   $1,015.94   $1,015.95   $1,015.90