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 $149.82   12.615%   $168.7198   $168.72   $168.70   $168.70  
  Purchase #2 $236.87   9.264%   $258.8136   $258.81   $258.80   $258.80  
  Purchase #3 $184.35   12.161%   $206.7688   $206.77   $206.75   $206.80  
  Purchase #4 $147.58   3.847%   $153.2574   $153.26   $153.25   $153.30  
  Purchase #5 $54.52   5.748%   $57.6538   $57.65   $57.65   $57.70  
  Purchase #6 $248.58   11.358%   $276.8137   $276.81   $276.80   $276.80  
  Purchase #7 $110.35   3.752%   $114.4903   $114.49   $114.50   $114.50  
  7 purchase totals = $1,132.07       $1,236.5174   $1,236.51   $1,236.45   $1,236.60