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 $67.57   5.728%   $71.4404   $71.44   $71.45   $71.40  
  Purchase #2 $177.54   4.508%   $185.5435   $185.54   $185.55   $185.50  
  Purchase #3 $29.27   4.771%   $30.6665   $30.67   $30.65   $30.70  
  Purchase #4 $96.94   6.177%   $102.928   $102.93   $102.95   $102.90  
  Purchase #5 $194.32   5.635%   $205.2699   $205.27   $205.25   $205.30  
  Purchase #6 $56.69   5.839%   $60.0001   $60.00   $60.00   $60.00  
  Purchase #7 $112.61   13.602%   $127.9272   $127.93   $127.95   $127.90  
  7 purchase totals = $734.94       $783.7756   $783.78   $783.80   $783.70