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 $93.99   7.460%   $101.0017   $101.00   $101.00   $101.00  
  Purchase #2 $185.98   10.698%   $205.8761   $205.88   $205.90   $205.90  
  Purchase #3 $110.81   3.153%   $114.3038   $114.30   $114.30   $114.30  
  Purchase #4 $190.88   9.257%   $208.5498   $208.55   $208.55   $208.50  
  Purchase #5 $68.69   6.492%   $73.1494   $73.15   $73.15   $73.10  
  Purchase #6 $23.62   13.545%   $26.8193   $26.82   $26.80   $26.80  
  Purchase #7 $78.77   10.245%   $86.84   $86.84   $86.85   $86.80  
  7 purchase totals = $752.74       $816.5401   $816.54   $816.55   $816.40