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 $34.68   8.238%   $37.5369   $37.54   $37.55   $37.50  
  Purchase #2 $61.89   3.337%   $63.9553   $63.96   $63.95   $64.00  
  Purchase #3 $248.53   7.103%   $266.1831   $266.18   $266.20   $266.20  
  Purchase #4 $212.45   8.839%   $231.2285   $231.23   $231.25   $231.20  
  Purchase #5 $36.67   5.201%   $38.5772   $38.58   $38.60   $38.60  
  Purchase #6 $93.94   3.742%   $97.4552   $97.46   $97.45   $97.50  
  Purchase #7 $217.39   5.564%   $229.4856   $229.49   $229.50   $229.50  
  7 purchase totals = $905.55       $964.4218   $964.44   $964.50   $964.50