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 $247.58   8.422%   $268.4312   $268.43   $268.45   $268.40  
  Purchase #2 $38.49   8.357%   $41.7066   $41.71   $41.70   $41.70  
  Purchase #3 $153.64   4.407%   $160.4109   $160.41   $160.40   $160.40  
  Purchase #4 $198.95   4.778%   $208.4558   $208.46   $208.45   $208.50  
  Purchase #5 $167.29   6.847%   $178.7443   $178.74   $178.75   $178.70  
  Purchase #6 $179.38   4.757%   $187.9131   $187.91   $187.90   $187.90  
  Purchase #7 $65.46   13.269%   $74.1459   $74.15   $74.15   $74.10  
  7 purchase totals = $1,050.79       $1,119.8078   $1,119.81   $1,119.80   $1,119.70