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 $208.54   13.202%   $236.0715   $236.07   $236.05   $236.10  
  Purchase #2 $75.93   9.802%   $83.3727   $83.37   $83.35   $83.40  
  Purchase #3 $210.68   10.173%   $232.1125   $232.11   $232.10   $232.10  
  Purchase #4 $236.95   12.760%   $267.1848   $267.18   $267.20   $267.20  
  Purchase #5 $106.87   7.582%   $114.9729   $114.97   $114.95   $115.00  
  Purchase #6 $175.86   4.861%   $184.4086   $184.41   $184.40   $184.40  
  Purchase #7 $248.97   6.458%   $265.0485   $265.05   $265.05   $265.00  
  7 purchase totals = $1,263.80       $1,383.1715   $1,383.16   $1,383.10   $1,383.20