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 $58.60   10.193%   $64.5731   $64.57   $64.55   $64.60  
  Purchase #2 $166.82   12.419%   $187.5374   $187.54   $187.55   $187.50  
  Purchase #3 $36.37   13.475%   $41.2709   $41.27   $41.25   $41.30  
  Purchase #4 $246.61   12.431%   $277.2661   $277.27   $277.25   $277.30  
  Purchase #5 $125.75   13.115%   $142.2421   $142.24   $142.25   $142.20  
  Purchase #6 $56.64   13.142%   $64.0836   $64.08   $64.10   $64.10  
  Purchase #7 $104.76   9.389%   $114.5959   $114.60   $114.60   $114.60  
  7 purchase totals = $795.55       $891.5691   $891.57   $891.55   $891.60