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 $191.32   8.699%   $207.9629   $207.96   $207.95   $208.00  
  Purchase #2 $31.89   9.123%   $34.7993   $34.80   $34.80   $34.80  
  Purchase #3 $127.65   7.569%   $137.3118   $137.31   $137.30   $137.30  
  Purchase #4 $53.96   6.106%   $57.2548   $57.25   $57.25   $57.30  
  Purchase #5 $115.56   11.510%   $128.861   $128.86   $128.85   $128.90  
  Purchase #6 $171.48   12.178%   $192.3628   $192.36   $192.35   $192.40  
  Purchase #7 $31.45   11.766%   $35.1504   $35.15   $35.15   $35.20  
  7 purchase totals = $723.31       $793.7030   $793.69   $793.65   $793.90