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 $30.55   13.212%   $34.5863   $34.59   $34.60   $34.60  
  Purchase #2 $218.54   10.521%   $241.5326   $241.53   $241.55   $241.50  
  Purchase #3 $57.96   13.150%   $65.5817   $65.58   $65.60   $65.60  
  Purchase #4 $90.81   8.678%   $98.6905   $98.69   $98.70   $98.70  
  Purchase #5 $6.55   8.783%   $7.1253   $7.13   $7.15   $7.10  
  Purchase #6 $226.56   8.485%   $245.7836   $245.78   $245.80   $245.80  
  Purchase #7 $248.57   7.500%   $267.2128   $267.21   $267.20   $267.20  
  7 purchase totals = $879.54       $960.5128   $960.51   $960.60   $960.50