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 $145.41   10.440%   $160.5908   $160.59   $160.60   $160.60  
  Purchase #2 $242.91   6.595%   $258.9299   $258.93   $258.95   $258.90  
  Purchase #3 $43.83   12.697%   $49.3951   $49.40   $49.40   $49.40  
  Purchase #4 $187.54   3.724%   $194.524   $194.52   $194.50   $194.50  
  Purchase #5 $48.76   9.431%   $53.3586   $53.36   $53.35   $53.40  
  Purchase #6 $83.77   12.717%   $94.423   $94.42   $94.40   $94.40  
  Purchase #7 $184.53   4.800%   $193.3874   $193.39   $193.40   $193.40  
  7 purchase totals = $936.75       $1,004.6088   $1,004.61   $1,004.60   $1,004.60