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 $226.80   8.473%   $246.0168   $246.02   $246.00   $246.00  
  Purchase #2 $191.32   11.381%   $213.0941   $213.09   $213.10   $213.10  
  Purchase #3 $90.76   7.546%   $97.6087   $97.61   $97.60   $97.60  
  Purchase #4 $123.58   13.451%   $140.2027   $140.20   $140.20   $140.20  
  Purchase #5 $220.61   3.403%   $228.1174   $228.12   $228.10   $228.10  
  Purchase #6 $196.35   5.646%   $207.4359   $207.44   $207.45   $207.40  
  Purchase #7 $122.91   4.358%   $128.2664   $128.27   $128.25   $128.30  
  7 purchase totals = $1,172.33       $1,260.7420   $1,260.75   $1,260.70   $1,260.70