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 $226.32   11.657%   $252.7021   $252.70   $252.70   $252.70  
  Purchase #2 $161.79   10.255%   $178.3816   $178.38   $178.40   $178.40  
  Purchase #3 $44.78   5.148%   $47.0853   $47.09   $47.10   $47.10  
  Purchase #4 $27.69   6.177%   $29.4004   $29.40   $29.40   $29.40  
  Purchase #5 $36.83   12.350%   $41.3785   $41.38   $41.40   $41.40  
  Purchase #6 $139.38   12.627%   $156.9795   $156.98   $157.00   $157.00  
  Purchase #7 $237.28   5.782%   $250.9995   $251.00   $251.00   $251.00  
  7 purchase totals = $874.07       $956.9269   $956.93   $957.00   $957.00