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 $25.86   3.678%   $26.8111   $26.81   $26.80   $26.80  
  Purchase #2 $232.71   12.452%   $261.687   $261.69   $261.70   $261.70  
  Purchase #3 $142.77   11.204%   $158.766   $158.77   $158.75   $158.80  
  Purchase #4 $199.92   5.838%   $211.5913   $211.59   $211.60   $211.60  
  Purchase #5 $109.27   5.770%   $115.5749   $115.57   $115.55   $115.60  
  Purchase #6 $172.37   3.315%   $178.0841   $178.08   $178.10   $178.10  
  Purchase #7 $101.60   5.606%   $107.2957   $107.30   $107.30   $107.30  
  7 purchase totals = $984.50       $1,059.8101   $1,059.81   $1,059.80   $1,059.90