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 $241.47   7.627%   $259.8869   $259.89   $259.90   $259.90  
  Purchase #2 $193.57   12.184%   $217.1546   $217.15   $217.15   $217.20  
  Purchase #3 $229.26   7.149%   $245.6498   $245.65   $245.65   $245.60  
  Purchase #4 $123.46   3.423%   $127.686   $127.69   $127.70   $127.70  
  Purchase #5 $111.85   5.124%   $117.5812   $117.58   $117.60   $117.60  
  Purchase #6 $58.94   11.367%   $65.6397   $65.64   $65.65   $65.60  
  Purchase #7 $231.65   4.469%   $242.0024   $242.00   $242.00   $242.00  
  7 purchase totals = $1,190.20       $1,275.6006   $1,275.60   $1,275.65   $1,275.60