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 $46.81   3.149%   $48.284   $48.28   $48.30   $48.30  
  Purchase #2 $224.65   12.631%   $253.0255   $253.03   $253.05   $253.00  
  Purchase #3 $161.83   9.104%   $176.563   $176.56   $176.55   $176.60  
  Purchase #4 $46.45   10.842%   $51.4861   $51.49   $51.50   $51.50  
  Purchase #5 $10.54   11.253%   $11.7261   $11.73   $11.75   $11.70  
  Purchase #6 $214.34   5.637%   $226.4223   $226.42   $226.40   $226.40  
  Purchase #7 $36.94   13.587%   $41.959   $41.96   $41.95   $42.00  
  7 purchase totals = $741.56       $809.4660   $809.47   $809.50   $809.50