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 $114.50   6.210%   $121.6105   $121.61   $121.60   $121.60  
  Purchase #2 $196.91   4.751%   $206.2652   $206.27   $206.25   $206.30  
  Purchase #3 $17.43   5.503%   $18.3892   $18.39   $18.40   $18.40  
  Purchase #4 $93.86   10.477%   $103.6937   $103.69   $103.70   $103.70  
  Purchase #5 $69.50   9.745%   $76.2728   $76.27   $76.25   $76.30  
  Purchase #6 $49.28   7.522%   $52.9868   $52.99   $53.00   $53.00  
  Purchase #7 $208.28   7.604%   $224.1176   $224.12   $224.10   $224.10  
  7 purchase totals = $749.76       $803.3358   $803.34   $803.30   $803.40