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 $197.48   5.205%   $207.7588   $207.76   $207.75   $207.80  
  Purchase #2 $17.71   5.142%   $18.6206   $18.62   $18.60   $18.60  
  Purchase #3 $188.28   5.606%   $198.835   $198.84   $198.85   $198.80  
  Purchase #4 $33.52   13.688%   $38.1082   $38.11   $38.10   $38.10  
  Purchase #5 $50.75   9.839%   $55.7433   $55.74   $55.75   $55.70  
  Purchase #6 $239.73   11.212%   $266.6085   $266.61   $266.60   $266.60  
  Purchase #7 $8.66   8.140%   $9.3649   $9.36   $9.35   $9.40  
  7 purchase totals = $736.13       $795.0393   $795.04   $795.00   $795.00