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 $203.43   9.136%   $222.0154   $222.02   $222.00   $222.00  
  Purchase #2 $239.26   8.420%   $259.4057   $259.41   $259.40   $259.40  
  Purchase #3 $231.51   12.181%   $259.7102   $259.71   $259.70   $259.70  
  Purchase #4 $56.48   8.808%   $61.4548   $61.45   $61.45   $61.50  
  Purchase #5 $171.48   6.168%   $182.0569   $182.06   $182.05   $182.10  
  Purchase #6 $195.85   3.376%   $202.4619   $202.46   $202.45   $202.50  
  Purchase #7 $60.26   8.861%   $65.5996   $65.60   $65.60   $65.60  
  7 purchase totals = $1,158.27       $1,252.7045   $1,252.71   $1,252.65   $1,252.80