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 $147.76   13.738%   $168.0593   $168.06   $168.05   $168.10  
  Purchase #2 $190.30   3.430%   $196.8273   $196.83   $196.85   $196.80  
  Purchase #3 $171.97   11.788%   $192.2418   $192.24   $192.25   $192.20  
  Purchase #4 $233.52   11.579%   $260.5593   $260.56   $260.55   $260.60  
  Purchase #5 $150.92   13.152%   $170.769   $170.77   $170.75   $170.80  
  Purchase #6 $237.99   9.318%   $260.1659   $260.17   $260.15   $260.20  
  Purchase #7 $140.71   3.409%   $145.5068   $145.51   $145.50   $145.50  
  7 purchase totals = $1,273.17       $1,394.1294   $1,394.14   $1,394.10   $1,394.20