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 $210.63   10.733%   $233.2369   $233.24   $233.25   $233.20  
  Purchase #2 $165.36   12.430%   $185.9142   $185.91   $185.90   $185.90  
  Purchase #3 $78.38   3.288%   $80.9571   $80.96   $80.95   $81.00  
  Purchase #4 $234.88   11.332%   $261.4966   $261.50   $261.50   $261.50  
  Purchase #5 $87.55   12.324%   $98.3397   $98.34   $98.35   $98.30  
  Purchase #6 $204.70   11.175%   $227.5752   $227.58   $227.60   $227.60  
  Purchase #7 $73.79   9.723%   $80.9646   $80.96   $80.95   $81.00  
  7 purchase totals = $1,055.29       $1,168.4843   $1,168.49   $1,168.50   $1,168.50