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 $249.94   10.671%   $276.6111   $276.61   $276.60   $276.60  
  Purchase #2 $75.77   10.466%   $83.7001   $83.70   $83.70   $83.70  
  Purchase #3 $116.65   13.874%   $132.834   $132.83   $132.85   $132.80  
  Purchase #4 $72.26   12.583%   $81.3525   $81.35   $81.35   $81.40  
  Purchase #5 $8.71   3.416%   $9.0075   $9.01   $9.00   $9.00  
  Purchase #6 $125.98   3.239%   $130.0605   $130.06   $130.05   $130.10  
  Purchase #7 $193.63   12.119%   $217.096   $217.10   $217.10   $217.10  
  7 purchase totals = $842.94       $930.6617   $930.66   $930.65   $930.70