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 $59.86   6.446%   $63.7186   $63.72   $63.70   $63.70  
  Purchase #2 $163.44   8.864%   $177.9273   $177.93   $177.95   $177.90  
  Purchase #3 $16.82   8.584%   $18.2638   $18.26   $18.25   $18.30  
  Purchase #4 $59.76   9.268%   $65.2986   $65.30   $65.30   $65.30  
  Purchase #5 $218.26   6.544%   $232.5429   $232.54   $232.55   $232.50  
  Purchase #6 $66.74   11.679%   $74.5346   $74.53   $74.55   $74.50  
  Purchase #7 $164.39   7.312%   $176.4102   $176.41   $176.40   $176.40  
  7 purchase totals = $749.27       $808.6960   $808.69   $808.70   $808.60