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 $57.92   8.105%   $62.6144   $62.61   $62.60   $62.60  
  Purchase #2 $232.49   7.549%   $250.0407   $250.04   $250.05   $250.00  
  Purchase #3 $218.90   13.193%   $247.7795   $247.78   $247.80   $247.80  
  Purchase #4 $97.87   5.852%   $103.5974   $103.60   $103.60   $103.60  
  Purchase #5 $210.86   5.821%   $223.1342   $223.13   $223.15   $223.10  
  Purchase #6 $23.90   10.124%   $26.3196   $26.32   $26.30   $26.30  
  Purchase #7 $104.58   9.227%   $114.2296   $114.23   $114.25   $114.20  
  7 purchase totals = $946.52       $1,027.7154   $1,027.71   $1,027.75   $1,027.60