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 $248.76   3.197%   $256.7129   $256.71   $256.70   $256.70  
  Purchase #2 $93.36   3.394%   $96.5286   $96.53   $96.55   $96.50  
  Purchase #3 $223.98   10.175%   $246.77   $246.77   $246.75   $246.80  
  Purchase #4 $54.96   4.373%   $57.3634   $57.36   $57.35   $57.40  
  Purchase #5 $23.72   4.418%   $24.7679   $24.77   $24.75   $24.80  
  Purchase #6 $237.51   4.673%   $248.6088   $248.61   $248.60   $248.60  
  Purchase #7 $5.91   10.724%   $6.5438   $6.54   $6.55   $6.50  
  7 purchase totals = $888.20       $937.2954   $937.29   $937.25   $937.30