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 $224.49   5.242%   $236.2578   $236.26   $236.25   $236.30  
  Purchase #2 $185.99   6.435%   $197.9585   $197.96   $197.95   $198.00  
  Purchase #3 $186.48   10.843%   $206.7   $206.70   $206.70   $206.70  
  Purchase #4 $119.90   3.853%   $124.5197   $124.52   $124.50   $124.50  
  Purchase #5 $44.36   8.770%   $48.2504   $48.25   $48.25   $48.30  
  Purchase #6 $72.78   4.720%   $76.2152   $76.22   $76.20   $76.20  
  Purchase #7 $91.37   5.741%   $96.6156   $96.62   $96.60   $96.60  
  7 purchase totals = $925.37       $986.5172   $986.53   $986.45   $986.60