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 $226.62   9.565%   $248.2962   $248.30   $248.30   $248.30  
  Purchase #2 $90.76   5.723%   $95.9542   $95.95   $95.95   $96.00  
  Purchase #3 $52.40   6.287%   $55.6944   $55.69   $55.70   $55.70  
  Purchase #4 $38.82   3.231%   $40.0743   $40.07   $40.05   $40.10  
  Purchase #5 $224.96   7.328%   $241.4451   $241.45   $241.45   $241.40  
  Purchase #6 $31.69   6.662%   $33.8012   $33.80   $33.80   $33.80  
  Purchase #7 $8.44   9.481%   $9.2402   $9.24   $9.25   $9.20  
  7 purchase totals = $673.69       $724.5056   $724.50   $724.50   $724.50