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 $87.38   5.792%   $92.441   $92.44   $92.45   $92.40  
  Purchase #2 $176.70   8.548%   $191.8043   $191.80   $191.80   $191.80  
  Purchase #3 $246.71   8.757%   $268.3144   $268.31   $268.30   $268.30  
  Purchase #4 $46.86   7.674%   $50.456   $50.46   $50.45   $50.50  
  Purchase #5 $93.30   4.276%   $97.2895   $97.29   $97.30   $97.30  
  Purchase #6 $44.58   9.298%   $48.725   $48.73   $48.75   $48.70  
  Purchase #7 $168.78   4.196%   $175.862   $175.86   $175.85   $175.90  
  7 purchase totals = $864.31       $924.8922   $924.89   $924.90   $924.90