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 $246.74   6.139%   $261.8874   $261.89   $261.90   $261.90  
  Purchase #2 $57.87   4.493%   $60.4701   $60.47   $60.45   $60.50  
  Purchase #3 $230.62   4.561%   $241.1386   $241.14   $241.15   $241.10  
  Purchase #4 $227.43   10.853%   $252.113   $252.11   $252.10   $252.10  
  Purchase #5 $136.40   7.774%   $147.0037   $147.00   $147.00   $147.00  
  Purchase #6 $227.80   7.755%   $245.4659   $245.47   $245.45   $245.50  
  Purchase #7 $186.59   7.267%   $200.1495   $200.15   $200.15   $200.10  
  7 purchase totals = $1,313.45       $1,408.2282   $1,408.23   $1,408.20   $1,408.20