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 $81.95   5.697%   $86.6187   $86.62   $86.60   $86.60  
  Purchase #2 $250.97   9.526%   $274.8774   $274.88   $274.90   $274.90  
  Purchase #3 $171.69   7.136%   $183.9418   $183.94   $183.95   $183.90  
  Purchase #4 $240.56   13.525%   $273.0957   $273.10   $273.10   $273.10  
  Purchase #5 $52.98   7.484%   $56.945   $56.95   $56.95   $56.90  
  Purchase #6 $114.80   12.158%   $128.7574   $128.76   $128.75   $128.80  
  Purchase #7 $25.71   9.686%   $28.2003   $28.20   $28.20   $28.20  
  7 purchase totals = $938.66       $1,032.4363   $1,032.45   $1,032.45   $1,032.40