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 $206.93   10.743%   $229.1605   $229.16   $229.15   $229.20  
  Purchase #2 $13.97   4.138%   $14.5481   $14.55   $14.55   $14.50  
  Purchase #3 $81.37   8.567%   $88.341   $88.34   $88.35   $88.30  
  Purchase #4 $235.48   4.259%   $245.5091   $245.51   $245.50   $245.50  
  Purchase #5 $210.76   3.765%   $218.6951   $218.70   $218.70   $218.70  
  Purchase #6 $28.44   7.327%   $30.5238   $30.52   $30.50   $30.50  
  Purchase #7 $114.88   7.301%   $123.2674   $123.27   $123.25   $123.30  
  7 purchase totals = $891.83       $950.0450   $950.05   $950.00   $950.00