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 $164.96   11.848%   $184.5045   $184.50   $184.50   $184.50  
  Purchase #2 $226.62   5.643%   $239.4082   $239.41   $239.40   $239.40  
  Purchase #3 $33.40   6.106%   $35.4394   $35.44   $35.45   $35.40  
  Purchase #4 $247.95   4.243%   $258.4705   $258.47   $258.45   $258.50  
  Purchase #5 $114.62   3.410%   $118.5285   $118.53   $118.55   $118.50  
  Purchase #6 $188.43   7.187%   $201.9725   $201.97   $201.95   $202.00  
  Purchase #7 $90.79   3.234%   $93.7261   $93.73   $93.75   $93.70  
  7 purchase totals = $1,066.77       $1,132.0497   $1,132.05   $1,132.05   $1,132.00