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 $16.26   8.764%   $17.685   $17.69   $17.70   $17.70  
  Purchase #2 $86.74   12.509%   $97.5903   $97.59   $97.60   $97.60  
  Purchase #3 $191.97   5.725%   $202.9603   $202.96   $202.95   $203.00  
  Purchase #4 $116.58   12.621%   $131.2936   $131.29   $131.30   $131.30  
  Purchase #5 $58.70   4.827%   $61.5334   $61.53   $61.55   $61.50  
  Purchase #6 $186.42   4.334%   $194.4994   $194.50   $194.50   $194.50  
  Purchase #7 $169.52   13.782%   $192.8832   $192.88   $192.90   $192.90  
  7 purchase totals = $826.19       $898.4452   $898.44   $898.50   $898.50