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 $232.61   12.285%   $261.1861   $261.19   $261.20   $261.20  
  Purchase #2 $92.87   6.327%   $98.7459   $98.75   $98.75   $98.70  
  Purchase #3 $101.64   11.293%   $113.1182   $113.12   $113.10   $113.10  
  Purchase #4 $178.89   8.619%   $194.3085   $194.31   $194.30   $194.30  
  Purchase #5 $132.30   13.252%   $149.8324   $149.83   $149.85   $149.80  
  Purchase #6 $120.90   8.715%   $131.4364   $131.44   $131.45   $131.40  
  Purchase #7 $248.36   10.433%   $274.2714   $274.27   $274.25   $274.30  
  7 purchase totals = $1,107.57       $1,222.8989   $1,222.91   $1,222.90   $1,222.80