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 $94.84   3.631%   $98.2836   $98.28   $98.30   $98.30  
  Purchase #2 $122.42   4.311%   $127.6975   $127.70   $127.70   $127.70  
  Purchase #3 $168.85   5.597%   $178.3005   $178.30   $178.30   $178.30  
  Purchase #4 $206.45   4.353%   $215.4368   $215.44   $215.45   $215.40  
  Purchase #5 $109.73   10.384%   $121.1244   $121.12   $121.10   $121.10  
  Purchase #6 $66.61   11.486%   $74.2608   $74.26   $74.25   $74.30  
  Purchase #7 $230.59   13.589%   $261.9249   $261.92   $261.90   $261.90  
  7 purchase totals = $999.49       $1,077.0285   $1,077.02   $1,077.00   $1,077.00