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 $18.45   3.211%   $19.0424   $19.04   $19.05   $19.00  
  Purchase #2 $116.83   7.812%   $125.9568   $125.96   $125.95   $126.00  
  Purchase #3 $202.39   9.825%   $222.2748   $222.27   $222.25   $222.30  
  Purchase #4 $80.63   5.490%   $85.0566   $85.06   $85.05   $85.10  
  Purchase #5 $86.32   5.197%   $90.8061   $90.81   $90.80   $90.80  
  Purchase #6 $130.50   3.372%   $134.9005   $134.90   $134.90   $134.90  
  Purchase #7 $65.61   3.627%   $67.9897   $67.99   $68.00   $68.00  
  7 purchase totals = $700.73       $746.0269   $746.03   $746.00   $746.10