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 $119.87   5.706%   $126.7098   $126.71   $126.70   $126.70  
  Purchase #2 $61.53   11.214%   $68.43   $68.43   $68.45   $68.40  
  Purchase #3 $93.69   12.108%   $105.034   $105.03   $105.05   $105.00  
  Purchase #4 $79.62   8.598%   $86.4657   $86.47   $86.45   $86.50  
  Purchase #5 $82.96   9.591%   $90.9167   $90.92   $90.90   $90.90  
  Purchase #6 $167.57   6.309%   $178.142   $178.14   $178.15   $178.10  
  Purchase #7 $41.83   10.491%   $46.2184   $46.22   $46.20   $46.20  
  7 purchase totals = $647.07       $701.9166   $701.92   $701.90   $701.80