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 $208.79   13.655%   $237.3003   $237.30   $237.30   $237.30  
  Purchase #2 $182.69   3.211%   $188.5562   $188.56   $188.55   $188.60  
  Purchase #3 $160.81   6.799%   $171.7435   $171.74   $171.75   $171.70  
  Purchase #4 $28.53   13.787%   $32.4634   $32.46   $32.45   $32.50  
  Purchase #5 $207.65   13.304%   $235.2758   $235.28   $235.30   $235.30  
  Purchase #6 $5.81   5.135%   $6.1083   $6.11   $6.10   $6.10  
  Purchase #7 $81.91   12.308%   $91.9915   $91.99   $92.00   $92.00  
  7 purchase totals = $876.19       $963.4390   $963.44   $963.45   $963.50