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 $87.83   9.571%   $96.2362   $96.24   $96.25   $96.20  
  Purchase #2 $145.99   12.148%   $163.7249   $163.72   $163.70   $163.70  
  Purchase #3 $116.58   5.194%   $122.6352   $122.64   $122.65   $122.60  
  Purchase #4 $43.39   7.475%   $46.6334   $46.63   $46.65   $46.60  
  Purchase #5 $244.78   6.778%   $261.3712   $261.37   $261.35   $261.40  
  Purchase #6 $42.76   8.797%   $46.5216   $46.52   $46.50   $46.50  
  Purchase #7 $180.88   8.548%   $196.3416   $196.34   $196.35   $196.30  
  7 purchase totals = $862.21       $933.4641   $933.46   $933.45   $933.30