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 $200.80   12.567%   $226.0345   $226.03   $226.05   $226.00  
  Purchase #2 $223.25   3.276%   $230.5637   $230.56   $230.55   $230.60  
  Purchase #3 $87.25   9.546%   $95.5789   $95.58   $95.60   $95.60  
  Purchase #4 $239.69   5.509%   $252.8945   $252.89   $252.90   $252.90  
  Purchase #5 $226.86   11.767%   $253.5546   $253.55   $253.55   $253.60  
  Purchase #6 $60.92   8.775%   $66.2657   $66.27   $66.25   $66.30  
  Purchase #7 $105.78   12.833%   $119.3547   $119.35   $119.35   $119.40  
  7 purchase totals = $1,144.55       $1,244.2466   $1,244.23   $1,244.25   $1,244.40