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 $32.61   3.155%   $33.6388   $33.64   $33.65   $33.60  
  Purchase #2 $178.63   13.381%   $202.5325   $202.53   $202.55   $202.50  
  Purchase #3 $56.76   8.291%   $61.466   $61.47   $61.45   $61.50  
  Purchase #4 $153.85   9.197%   $167.9996   $168.00   $168.00   $168.00  
  Purchase #5 $227.53   6.276%   $241.8098   $241.81   $241.80   $241.80  
  Purchase #6 $89.37   3.296%   $92.3156   $92.32   $92.30   $92.30  
  Purchase #7 $184.57   11.668%   $206.1056   $206.11   $206.10   $206.10  
  7 purchase totals = $923.32       $1,005.8679   $1,005.88   $1,005.85   $1,005.80