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 $114.26   8.717%   $124.22   $124.22   $124.20   $124.20  
  Purchase #2 $122.48   6.342%   $130.2477   $130.25   $130.25   $130.20  
  Purchase #3 $65.68   3.114%   $67.7253   $67.73   $67.75   $67.70  
  Purchase #4 $198.64   13.852%   $226.1556   $226.16   $226.15   $226.20  
  Purchase #5 $234.30   13.261%   $265.3705   $265.37   $265.35   $265.40  
  Purchase #6 $76.83   6.475%   $81.8047   $81.80   $81.80   $81.80  
  Purchase #7 $154.86   12.351%   $173.9868   $173.99   $174.00   $174.00  
  7 purchase totals = $967.05       $1,069.5106   $1,069.52   $1,069.50   $1,069.50