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 $65.61   5.545%   $69.2481   $69.25   $69.25   $69.20  
  Purchase #2 $18.61   13.481%   $21.1188   $21.12   $21.10   $21.10  
  Purchase #3 $226.34   13.759%   $257.4821   $257.48   $257.50   $257.50  
  Purchase #4 $49.57   8.149%   $53.6095   $53.61   $53.60   $53.60  
  Purchase #5 $73.90   4.616%   $77.3112   $77.31   $77.30   $77.30  
  Purchase #6 $245.76   9.243%   $268.4756   $268.48   $268.50   $268.50  
  Purchase #7 $65.71   3.133%   $67.7687   $67.77   $67.75   $67.80  
  7 purchase totals = $745.50       $815.0140   $815.02   $815.00   $815.00