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 $198.57   6.713%   $211.9   $211.90   $211.90   $211.90  
  Purchase #2 $18.81   4.144%   $19.5895   $19.59   $19.60   $19.60  
  Purchase #3 $127.61   5.779%   $134.9846   $134.98   $135.00   $135.00  
  Purchase #4 $151.35   4.134%   $157.6068   $157.61   $157.60   $157.60  
  Purchase #5 $163.99   13.553%   $186.2156   $186.22   $186.20   $186.20  
  Purchase #6 $243.79   6.752%   $260.2507   $260.25   $260.25   $260.30  
  Purchase #7 $26.61   6.678%   $28.387   $28.39   $28.40   $28.40  
  7 purchase totals = $930.73       $998.9342   $998.94   $998.95   $999.00