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 $231.25   13.294%   $261.9924   $261.99   $262.00   $262.00  
  Purchase #2 $250.33   12.689%   $282.0944   $282.09   $282.10   $282.10  
  Purchase #3 $33.59   3.534%   $34.7771   $34.78   $34.80   $34.80  
  Purchase #4 $39.29   13.778%   $44.7034   $44.70   $44.70   $44.70  
  Purchase #5 $77.35   11.461%   $86.2151   $86.22   $86.20   $86.20  
  Purchase #6 $148.91   13.160%   $168.5066   $168.51   $168.50   $168.50  
  Purchase #7 $48.42   10.672%   $53.5874   $53.59   $53.60   $53.60  
  7 purchase totals = $829.14       $931.8764   $931.88   $931.90   $931.90