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 $239.31   11.871%   $267.7185   $267.72   $267.70   $267.70  
  Purchase #2 $33.77   8.721%   $36.7151   $36.72   $36.70   $36.70  
  Purchase #3 $168.87   9.509%   $184.9278   $184.93   $184.95   $184.90  
  Purchase #4 $83.76   4.228%   $87.3014   $87.30   $87.30   $87.30  
  Purchase #5 $151.77   10.795%   $168.1536   $168.15   $168.15   $168.20  
  Purchase #6 $11.86   13.431%   $13.4529   $13.45   $13.45   $13.50  
  Purchase #7 $36.91   10.283%   $40.7055   $40.71   $40.70   $40.70  
  7 purchase totals = $726.25       $798.9748   $798.98   $798.95   $799.00