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 $85.49   13.656%   $97.1645   $97.16   $97.15   $97.20  
  Purchase #2 $182.99   6.377%   $194.6593   $194.66   $194.65   $194.70  
  Purchase #3 $129.51   11.407%   $144.2832   $144.28   $144.30   $144.30  
  Purchase #4 $238.38   4.348%   $248.7448   $248.74   $248.75   $248.70  
  Purchase #5 $196.84   6.382%   $209.4023   $209.40   $209.40   $209.40  
  Purchase #6 $131.52   4.490%   $137.4252   $137.43   $137.45   $137.40  
  Purchase #7 $34.34   9.533%   $37.6136   $37.61   $37.60   $37.60  
  7 purchase totals = $999.07       $1,069.2929   $1,069.28   $1,069.30   $1,069.30