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 $61.28   3.566%   $63.4652   $63.47   $63.45   $63.50  
  Purchase #2 $14.85   9.724%   $16.294   $16.29   $16.30   $16.30  
  Purchase #3 $106.91   11.446%   $119.1469   $119.15   $119.15   $119.10  
  Purchase #4 $59.73   8.186%   $64.6195   $64.62   $64.60   $64.60  
  Purchase #5 $133.60   13.566%   $151.7242   $151.72   $151.70   $151.70  
  Purchase #6 $207.64   13.359%   $235.3786   $235.38   $235.40   $235.40  
  Purchase #7 $186.98   4.381%   $195.1716   $195.17   $195.15   $195.20  
  7 purchase totals = $770.99       $845.8000   $845.80   $845.75   $845.80