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 $198.99   13.703%   $226.2576   $226.26   $226.25   $226.30  
  Purchase #2 $47.48   12.247%   $53.2949   $53.29   $53.30   $53.30  
  Purchase #3 $58.95   12.520%   $66.3305   $66.33   $66.35   $66.30  
  Purchase #4 $114.28   10.460%   $126.2337   $126.23   $126.25   $126.20  
  Purchase #5 $168.45   7.484%   $181.0568   $181.06   $181.05   $181.10  
  Purchase #6 $73.36   9.428%   $80.2764   $80.28   $80.30   $80.30  
  Purchase #7 $108.32   5.573%   $114.3567   $114.36   $114.35   $114.40  
  7 purchase totals = $769.83       $847.8066   $847.81   $847.85   $847.90