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 $25.53   3.173%   $26.3401   $26.34   $26.35   $26.30  
  Purchase #2 $194.26   9.346%   $212.4155   $212.42   $212.40   $212.40  
  Purchase #3 $56.34   12.761%   $63.5295   $63.53   $63.55   $63.50  
  Purchase #4 $84.81   4.202%   $88.3737   $88.37   $88.35   $88.40  
  Purchase #5 $104.92   9.126%   $114.495   $114.50   $114.50   $114.50  
  Purchase #6 $10.54   4.430%   $11.0069   $11.01   $11.00   $11.00  
  Purchase #7 $183.72   5.522%   $193.865   $193.87   $193.85   $193.90  
  7 purchase totals = $660.12       $710.0257   $710.04   $710.00   $710.00