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 $86.84   11.683%   $96.9855   $96.99   $97.00   $97.00  
  Purchase #2 $226.53   11.674%   $252.9751   $252.98   $253.00   $253.00  
  Purchase #3 $22.62   9.127%   $24.6845   $24.68   $24.70   $24.70  
  Purchase #4 $113.76   5.105%   $119.5674   $119.57   $119.55   $119.60  
  Purchase #5 $163.65   4.337%   $170.7475   $170.75   $170.75   $170.70  
  Purchase #6 $176.64   9.243%   $192.9668   $192.97   $192.95   $193.00  
  Purchase #7 $70.29   9.413%   $76.9064   $76.91   $76.90   $76.90  
  7 purchase totals = $860.33       $934.8332   $934.85   $934.85   $934.90