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 $100.61   12.373%   $113.0585   $113.06   $113.05   $113.10  
  Purchase #2 $210.83   13.753%   $239.8254   $239.83   $239.85   $239.80  
  Purchase #3 $30.70   11.302%   $34.1697   $34.17   $34.15   $34.20  
  Purchase #4 $224.42   11.705%   $250.6884   $250.69   $250.70   $250.70  
  Purchase #5 $235.70   5.659%   $249.0383   $249.04   $249.05   $249.00  
  Purchase #6 $153.79   12.241%   $172.6154   $172.62   $172.60   $172.60  
  Purchase #7 $6.91   10.186%   $7.6139   $7.61   $7.60   $7.60  
  7 purchase totals = $962.96       $1,067.0096   $1,067.02   $1,067.00   $1,067.00