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 $25.94   3.517%   $26.8523   $26.85   $26.85   $26.90  
  Purchase #2 $231.59   11.848%   $259.0288   $259.03   $259.05   $259.00  
  Purchase #3 $9.77   12.118%   $10.9539   $10.95   $10.95   $11.00  
  Purchase #4 $213.61   3.783%   $221.6909   $221.69   $221.70   $221.70  
  Purchase #5 $238.58   5.688%   $252.1504   $252.15   $252.15   $252.20  
  Purchase #6 $54.88   3.758%   $56.9424   $56.94   $56.95   $56.90  
  Purchase #7 $59.64   6.727%   $63.652   $63.65   $63.65   $63.70  
  7 purchase totals = $834.01       $891.2707   $891.26   $891.30   $891.40