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 $162.83   13.491%   $184.7974   $184.80   $184.80   $184.80  
  Purchase #2 $6.30   9.828%   $6.9192   $6.92   $6.90   $6.90  
  Purchase #3 $219.94   9.705%   $241.2852   $241.29   $241.30   $241.30  
  Purchase #4 $33.91   5.715%   $35.848   $35.85   $35.85   $35.80  
  Purchase #5 $43.66   3.469%   $45.1746   $45.17   $45.15   $45.20  
  Purchase #6 $224.40   10.694%   $248.3973   $248.40   $248.40   $248.40  
  Purchase #7 $207.30   3.508%   $214.5721   $214.57   $214.55   $214.60  
  7 purchase totals = $898.34       $976.9938   $977.00   $976.95   $977.00