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 $230.45   13.429%   $261.3971   $261.40   $261.40   $261.40  
  Purchase #2 $241.49   4.835%   $253.166   $253.17   $253.15   $253.20  
  Purchase #3 $40.94   8.664%   $44.487   $44.49   $44.50   $44.50  
  Purchase #4 $180.41   8.244%   $195.283   $195.28   $195.30   $195.30  
  Purchase #5 $165.39   7.721%   $178.1598   $178.16   $178.15   $178.20  
  Purchase #6 $142.88   10.633%   $158.0724   $158.07   $158.05   $158.10  
  Purchase #7 $191.62   3.851%   $198.9993   $199.00   $199.00   $199.00  
  7 purchase totals = $1,193.18       $1,289.5646   $1,289.57   $1,289.55   $1,289.70