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 $48.43   13.664%   $55.0475   $55.05   $55.05   $55.00  
  Purchase #2 $249.70   6.309%   $265.4536   $265.45   $265.45   $265.50  
  Purchase #3 $80.51   3.466%   $83.3005   $83.30   $83.30   $83.30  
  Purchase #4 $214.50   10.173%   $236.3211   $236.32   $236.30   $236.30  
  Purchase #5 $46.42   12.323%   $52.1403   $52.14   $52.15   $52.10  
  Purchase #6 $81.57   5.469%   $86.0311   $86.03   $86.05   $86.00  
  Purchase #7 $200.54   8.407%   $217.3994   $217.40   $217.40   $217.40  
  7 purchase totals = $921.67       $995.6935   $995.69   $995.70   $995.60