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 $57.78   8.664%   $62.7861   $62.79   $62.80   $62.80  
  Purchase #2 $231.96   13.186%   $262.5462   $262.55   $262.55   $262.50  
  Purchase #3 $164.45   10.157%   $181.1532   $181.15   $181.15   $181.20  
  Purchase #4 $201.91   8.203%   $218.4727   $218.47   $218.45   $218.50  
  Purchase #5 $7.83   8.284%   $8.4786   $8.48   $8.50   $8.50  
  Purchase #6 $105.99   10.583%   $117.2069   $117.21   $117.20   $117.20  
  Purchase #7 $101.48   12.233%   $113.894   $113.89   $113.90   $113.90  
  7 purchase totals = $871.40       $964.5377   $964.54   $964.55   $964.60