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 $208.77   12.872%   $235.6429   $235.64   $235.65   $235.60  
  Purchase #2 $185.92   3.619%   $192.6484   $192.65   $192.65   $192.60  
  Purchase #3 $234.76   7.143%   $251.5289   $251.53   $251.55   $251.50  
  Purchase #4 $57.95   10.584%   $64.0834   $64.08   $64.10   $64.10  
  Purchase #5 $183.76   13.435%   $208.4482   $208.45   $208.45   $208.40  
  Purchase #6 $41.49   4.296%   $43.2724   $43.27   $43.25   $43.30  
  Purchase #7 $16.53   4.786%   $17.3211   $17.32   $17.30   $17.30  
  7 purchase totals = $929.18       $1,012.9453   $1,012.94   $1,012.95   $1,012.80