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 $198.41   4.845%   $208.023   $208.02   $208.00   $208.00  
  Purchase #2 $242.85   13.604%   $275.8873   $275.89   $275.90   $275.90  
  Purchase #3 $156.69   9.624%   $171.7698   $171.77   $171.75   $171.80  
  Purchase #4 $242.73   8.228%   $262.7018   $262.70   $262.70   $262.70  
  Purchase #5 $96.63   12.117%   $108.3387   $108.34   $108.35   $108.30  
  Purchase #6 $110.88   12.523%   $124.7655   $124.77   $124.75   $124.80  
  Purchase #7 $208.55   7.732%   $224.6751   $224.68   $224.70   $224.70  
  7 purchase totals = $1,256.74       $1,376.1612   $1,376.17   $1,376.15   $1,376.20