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 $14.92   9.420%   $16.3255   $16.33   $16.35   $16.30  
  Purchase #2 $173.67   5.109%   $182.5428   $182.54   $182.55   $182.50  
  Purchase #3 $25.28   5.382%   $26.6406   $26.64   $26.65   $26.60  
  Purchase #4 $143.74   8.843%   $156.4509   $156.45   $156.45   $156.50  
  Purchase #5 $181.81   7.686%   $195.7839   $195.78   $195.80   $195.80  
  Purchase #6 $95.90   3.182%   $98.9515   $98.95   $98.95   $99.00  
  Purchase #7 $45.33   4.793%   $47.5027   $47.50   $47.50   $47.50  
  7 purchase totals = $680.65       $724.1979   $724.19   $724.25   $724.20