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 $49.50   9.557%   $54.2307   $54.23   $54.25   $54.20  
  Purchase #2 $245.62   6.752%   $262.2043   $262.20   $262.20   $262.20  
  Purchase #3 $230.50   10.408%   $254.4904   $254.49   $254.50   $254.50  
  Purchase #4 $69.44   3.821%   $72.0933   $72.09   $72.10   $72.10  
  Purchase #5 $196.64   4.866%   $206.2085   $206.21   $206.20   $206.20  
  Purchase #6 $42.34   5.372%   $44.6145   $44.61   $44.60   $44.60  
  Purchase #7 $32.63   11.655%   $36.433   $36.43   $36.45   $36.40  
  7 purchase totals = $866.67       $930.2747   $930.26   $930.30   $930.20