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 $91.77   4.176%   $95.6023   $95.60   $95.60   $95.60  
  Purchase #2 $231.98   13.189%   $262.5758   $262.58   $262.60   $262.60  
  Purchase #3 $8.34   6.608%   $8.8911   $8.89   $8.90   $8.90  
  Purchase #4 $93.99   3.376%   $97.1631   $97.16   $97.15   $97.20  
  Purchase #5 $33.48   12.762%   $37.7527   $37.75   $37.75   $37.80  
  Purchase #6 $183.37   13.248%   $207.6629   $207.66   $207.65   $207.70  
  Purchase #7 $92.82   13.677%   $105.515   $105.52   $105.50   $105.50  
  7 purchase totals = $735.75       $815.1629   $815.16   $815.15   $815.30